Electric cooker troubleshooting and repair book

Electric cooker and oven repair, work safely

Having been shocked in the past, I now take safety very seriously. Electricity can kill or harm you so never take any chances and ensure you never work on live equipment there is no need to do it and it will harm you eventually.

Never work alone with electrics if possible 

Never work on live equipment 

Always lock off the main circuit breaker to the circuit and ensure nobody else can turn it back on again.

Always test to ensure electrical equipment is dead by first testing on a known live to ensure your test gear is working then testing to prove the unit, then test to ensure the electric has successfully been isolated and the shower unit is dead, and now retest to ensure test gear is still working ok. (this isolation procedure is required under the electricity at work act)

Cooker oven repair – What is inside cooker oven and what are the components and parts

The model of cooker I am working on today is a Bush yours may differ there is not a lot I can do about that but most of the parts will be very similar so use this as a guide not as an exact manual for your repair.

This is a ceramic hob cooker with twin oven the bottom oven has one element and light bulb and is fan assisted.

The upper oven is a grill / oven and has an element that does both functions but this is a single element version some do have a separate element for both grill and oven use built into one part.

So here are some photos of the outside of the cooker I am working on.

Ceramic hob / switch panel and double ovens on front.

Here you can see 2 rear panels that give you access to the inside

of the rear on ovens and access to test elements and other stuff.

This is the top inspection panel removed and you see the wiring the 

single element in the upper centre and the over limit thermal cut off thermostat

on the silver metal rail on left of photo

close up of wiring connections of the upper oven heating element 

it has power connections an earthing point and a thermostat

this is the thermal cut out over limit thermostat 

This is the oven with bottom rear access panel removed 

the upper left-hand component it the light for inside oven

the item on the upper right is another thermal cut out over limit 

thermostat. Just below this is the main oven element connections and 

in the centre is the main oven fan motor.

Ill photo these close up now.

the oven light with its connections positive and negative and

an earth point for electrical protection.

close up of the lower oven over limit temperature device 

The lower oven main element connections 

The oven fan motor and its electrical connections.

Now move onto the upper hob they are all different in the way you get into them and In-fact this one is a terrible version as replacing the ceramic elements is very difficult to realign them correctly.

so I first undo any retaining screws and all are different so cannot help you exactly on your model best to get the manual.

The underside of the hob unit the metal cover unscrews and the elements are them lose

to change but beware this type are hard to refit as it can take ages to realign the elements correctly.

Quick peak into all the connections there are four elements on this one 

and a lot of wires 

these are the pins that need aligning on refitting looks easy but it can be 

very hard to align them all correctly i Tipex the tips of the and the holes 

so I know where they fit.

With the hob removed you can now access the switch panel here you can change switches and or thermostats.

Thermostats and switches, ensure you note and photo the wiring on the one you need to replace.

you need to remove the screws from the front panel 

and lastly the lcd display and timer panel electronics PCB.

see video of all this below 

Electric cooker oven ceramic hob repair , what is inside and what parts components

Cooker oven hob repair -  common problems and troubleshooting

Common cooker oven hob problems faults and fixes 

Overheating and food burning - could be a symptom of a faulty thermostat 

No heat - could be a sign the element is faulty but best to test the element just in case you have a faulty switch or thermostat.

No fan assist - probably a faulty fan motor test the coils of the motor and ensure fan it working ok if not replace.

Cooker oven hob knobs melting - could be sign your seal has gone around the oven door and this could need replacing.

Loud sound from oven - could be a failure in the electric fan check the fan and the fan blade out for signs if damage or being bent.

Oven light is out - change bulb the bulb has probably burned out 

Oven cuts off after a period of time, it could be the overheat limit thermostats turning the elements off after a overheat condition.

Cooker oven repair - replacing a broken selector switch knob

It is not that easy to test these but if it is not working and you have tested the elements we can safely assume it needs replacing, it is a very easy job in fact getting access to the switch is harder, in this I had to undo 3 screws holding the switch panel in place and remove all the switch selector knobs pull the switch panel free a couple of centimetres and access and remove the front 2 ceramic hob retaining screws, I then had to remove the ceramic hob holder brackets at rear of the hob and it pulls away just enough to give access to the rear and connect side of switches.

And this is where I start to photo what I did to fix this cooker.

So this is where the access for screws are on this cooker 

2 screw just undo them and screw with pull free from back hopefully

giving you enough room to check the terminations on the rear of switch unit 

I have pulled indicator lamp of here to save disconnecting it from switch 

here is the switch back and all connections best to photo it for 

replacement and to save issues and its also marked TOP so you know which way around it goes

there are 2 reds and 2 browns so I mark the second red and brown with black ink to

show me which ones are which and them basically go around and write down which 

wire colours go to which number terminal

So here the double brown goes to terminal P1 an red 1 goes to terminal 2

and so here I wrote my terminations list in below photo

Once this is done pull the wires off and replace switch unit 

see video below of this entire process.

Electric cooker oven ceramic hob repair - switches switch replacement

Testing electric cooker oven thermostat with multimeter

an easy test to do getting into the thermostat is the hardest part and then locating the wires to test on this machine you need to remove the top hob to access the switches and thermostats.

to remove the hob top remove rear brackets and undo front retaining screws yours may differ

Remove panel switches

Locate the thermostat and the correct wires going to element 

Now turn the thermostat switch on and off you should have OL when switch is off and low ohm continuity when off 

see video of this process below 

Electric cooker oven ceramic hob element testing and replacement

This is not an hard job but it can be made more difficult by bad design and on this particular model it is made more difficult than it really should be , on refitting you have to align the pins in the correct places to made the metal outer shroud to fit correctly. Unfortunately changing one moves all of them and it can take a while to realign the ceramic elements into position for it all to fit together nicely. I always mare the holes that the pins come from so that is one problem solved i usually tipex the tips of the element fitment pins so I can see them easier but today typically I had ran out so made it a little harder on myself.

Undo the retaining screws from around the outside of the 

housing shroud and then you can lift the shroud up 

you get just enough room to sneak a ceramic element out but it tight 

and you will move all of them and have to realign the fitting pins 

see photo below for fitting pins and I have marked next to them 

in black marker pen to show me which holes the pins align to

as the manufacturer kindly drilled loads of holes just to confuse matters 

fitting pins and marking the holes with marker pen for realignment purposes

You can remove this earth it is the only wire you can remove and it gets it out of the way at least 

undo retaining screws

photo and write down wire connectors so you will not make a mistake when you refit 

below is a photo of my connections notes to make this easier for myself 

lift up the housing shroud and you can see all the ceramic elements 

i am choosing the easiest to get to if yours is faulty you will not have much choice 

here is the element removed and free 

Here Iam testing the element for continuity set multimeter to ohms 

and test on the 2 connections closest to the element and make sure it is the correct

one, if you get a reading here I get 26 ohms your element is intact and good. If no reading you will have to replace it.

I am going to slide the element back in place and reconnect the wiring connections

wires all connected and attempting to realign the housing fitment pins with holes 

Job done all pins aligned and ready to refit hob back 

it took me 20 mins to realign pins.

See video of this process below

Electric cooker oven ceramic hob element testing

Cooker oven hob repair - changing replacing and testing,  grill / oven cooker element with built in capillary tube thermostat 

This is on the top upper oven on this twin cavity oven cooker model.

Not a hard job just 2 wires and 2 screw on this model and most models to be fair but this one does make it a bit more difficult that you have to open up the copper tube holding element and pull it out it can be hard to get the capillary tube out, try to open the copper out carefully and steady. Try not to damage capillary tube as you may cause damage and further expense and time on repair.

to begin with gain access to the rear of element you will need to access both front and rear

Remove the wiring but make not of what goes where so you return them back to 

how they were before and remove the protective earth connection to 

Now open up the capillary tube copper shroud its inside this copper tube

you need to use long nose pliers and open up the tube to allow the probe to 

be pulled out from inside

probe is now out you can go to front of the oven open the door and look for the screws that

hold the element in place 

both retaining screws removed the element will just pull free 

Element is out you can test it with the multimeter again if you wish and test new on prior to fitting 

now refit make sure all holes are aligned and then screw in retaining screws

rethread the thermostat capillary tube back into its shroud and bend copper 

a bit so it will not work free

reattach the wiring connectors 

Cooker oven hob repair changing replacing and testing, grill oven cooker element with built in c - YouTube

Cooker oven hob repair, testing and replacing thermal cut out overload over limit thermostats

Very easy job to both replace and test these just a screwdriver to undo the back panel to gain access to the terminations and a basic multimeter. You should get very low ohms reading as it is just a thermostatically controlled switch basically and should be on all the time it will only open the circuit if the temperature goes about a set perimeter which is usually stamped on the device itself.

Symptoms would be no power to oven at all or just will not get hot, but test first and test elements as well to ensure you replace correct part.

With back access panels removed you can see the 2 over limit thermostats

they have blue wires going to them ill show close ups below 

close ups of both upper oven and main oven thermal

over limit cut out thermostats 

Pull of both cables and you can test it for continuity 

it should be very low ohms resistance reading as this is 

just a safety switch and should be on at all times.

testing with a multimeter 0.0 ohms so excellent 

and continuity buzzer is buzzing see video for this 

this one is held in by one screw and the other side fits into a bracket made for it 

this is the unit free from oven and easy to replace 

testing new thermal cut out over limit thermostat prior to fitting 

just one screw so easy to do 

see a video of this process below 

Cooker oven hob repair , testing and replacing thermal cut out overload over limit thermostats

Electric cooker oven hob repair, testing and replacing the main oven element

The  main oven element on this twin cavity oven cooker is wired from the rear but must be unscrewed from inside the oven after removing the fan cover. to test it you just need to continuity test but you can take an ohms reading visit and power calculator online to get the power and make sure yours matches. So firstly i removed the back cover to access the wiring and then i test the element obviously this one is good but yours may be OL on the multimeter which shows it is damaged and not a complete circuit so needs replacing.

Mine showed 230V  ( UK voltage ) squared / 25.9 Resistance = 2KW Power 

Before starting ensure oven is isolated from electricity never work on live equipment.

identify the correct cables and remove connectors 

now connectors are removed set the multmeter to ohms 

and connect multimeter probes to terminals 

my reading is 25.9 this is a perfect reading for a 2kw cooker oven element 

Ill carry on a replace this anyway to show you the steps your may differ slightly 

but the principles are the same 

remove the fan and element cover 

then undo the electric element retaining screws 

and the element should pull away easily 

here i test the element again outside the oven its 26.1 now 

but these meters are not always exact so its still a good reading 

now replace the new element 

screw in both retaining screws

make sure the fan is central to the element and tighten  

and finally refit the our fan / element cover

and then refit the electric connections to the rear of the element 

exactly as you found them 

You can see the video below of this process 

Electric cooker oven hob repair , testing and replacing the main oven element - YouTube

Electric cooker oven hob repair, testing and changing light bulb in cooker oven

The bulb is just an element the same as the oven element so easy to test just continuity test it to make sure element is intact if it is you have a contact issues maybe bulb is not screw in enough or terminals are dirty. But mostly a bulb is going to blow after so many hours of use.  you need to get to the rear of bulb via the rear access panel to test it but you can just change it from inside the oven if you want to.

Here are the steps blow to change a light bulb in a cooker oven 

if you want to test bulb from rear pull of the connections 

connect multimeter and set to continuity ohms reading 

a reading shows the bulb as good but I will show replacement anyway 

look for the glass bulb cover it should screw off 

to reveal the bulb now unscrew the bulb 

then screw in new bulb and screw in the glass cover to protect bulb etc from oven heat 

See video of this below

https://youtu.be/4OEGq-AmrrE

Electric cooker, oven Fan failure or noise,  testing winding and inspecting rotor and replacement

Sometimes the fan will stop working or it can make loud noises due to motor damage, bearing failure or warping of the fan blades. The only way to find out is to dismantle and inspect the whole fan assembly.

I started out by removing the back cover and locating the motor for the fan, i then tested the motor for continuity within the motor field windings and this being a good motor and fan unit the reading was good, if you get OL then the windings have failed so you need to replace these.

Unfortunately, the locking nut on the fan blade was too tight under normal circumstances I would if cut the rotor in half with a grinder, hack saw or reciprocating saw and replaced but seeing as this is a good unit i decided to leave it in place not good for this post but best I could do.

I just removed the winding if you winding are damaged and your rotor fits exactly into replacement then you could consider just replacing this piece and leaving the rotor and fan blades as they are.

locate fan and you may need to pull up the connector or remove completely 

connect the multimeter and select ohms continuity reading 

here i remove the fan and element cover to access the fan blades

I tried a spanner and socket but could not get the retaining bolt to budge 

even tried wd40 and leverage but it was not budging, usually I would cut the nut off with a 

grinder but this is a good unit so did not want to damage it 

instead, you could dismantle from the rear and either cut rotor in half or 

just replace the winding if that is all the is faulty.

undoing screws and below the rear rotor mount and bearing assembly 

you can see rotor here now and winding will pull free 

here is the fan motor winding you could just unplug the connectors

and replace this unit on its own 

Above is rotor assembly 

and below I start the process of refitting the winding

and the motor housing 

tightening up the rear rotor mount and bearing

and then below the motor housing retaining screws

see below for video of this process 

https://youtu.be/bHFpWM2aDK4

Cooker oven hob repairs how to remove and refit oven cooker door

It can be different on some models but this seem to be the most popular way to fit oven door for easy removal for service and cleaning.

You need to pen door fully pull back the retaining clips or locking tabs and then close door until the hindge becomes free in body it should then just pull free.

open door to access the hinge locking tabs 

open up locking tabs fully on both hinge sides 

now close door so it free hinge and door should pull free 

Now replace in reverse order push hinges into mounting holes 

Close locking tabs and then open and close door a few times to ensure everything is safe  

See video of this process below 

https://www.youtube.com/watch?v=wtC7MDfymQ0

Microwave cooker oven - whats inside

Just found a scrap microwave on the street so lets take to pieces and learn something if we can , never took one apart although i did study them at college for my Electrical engineering course but not in any great detail.

Beware they have very large capacitor inside with high voltage and its enough to kill so make sure you discharge this prior to touching anything inside.

The cover comes off easy just 8-9 screws around the outside edges and we can now see what is inside.

Here is the incoming mains connections looks like 

some input protection and filtering going on it 

The capacitor is large and must be discharged prior to working on these machines the wires attached to cap are secondary transformer 

wires and a diode ( high voltage )

In the centre the magnetron this creates the microwaves for cooking 

some good videos on Youtube regards how they work.

Below this is the transformer and this can be tested easily

To left of this photo is the main control PCB board 

and just behind the PCB are three micro switches which are triple safety devices for ensuring 

door is shut prior to machine operating so you cannot accidently microwave yourself 

and on top to the left the light bulb and centre the thermal cut out protecting unit from overheating 

Microwave oven - troubleshooting fault finding and repair

First i test the mains cable from the pin on the plug to the terminal on the incoming mains PCB board inside the microwave, first set multimeter to read ohms continuity and you should get very low ohms reading if you OL you have faulty cable or fuse has blown is either plug or internal to microwave. 

Actually first thing is to discharge capacitor to void injury

Short out the terminals of the capacitor with an insulated set of pliers.

Here i test the live both sides of internal fuse so i am testing the fuse as well 

and then do the same on the neutral pin to neutral terminal on PCB board

if you get

Below i am testing the thermal cut out its easy to get to and easy to do so my as well do it now 

Below i am testing the bulb this is 141.6 ohm so very good 

not an essential test but easy to do and again easy to get to 

Now ill test the door micro switches there are three of them and they provide 

protection preventing the microwave operating when door is open and any 

risk of exposure from the waves , so very important these work correctly s 

they can turn off power to the primary side of winding preventing it working

as you can see with door closed the switch is on and low continuity

with the door open the switch turns off and meter should red OL 

beware some switches may be the opposite and turn open when open 

Test ll three micro switches and ensure the same results are seen

closed

open

last one with the door closed we have  reading on multimeter 

close up of connections to microswitch 

and door open the switch is open and multimeter shows OL 

Now i test the primary winding side of the transformer 

Primary winding was 3.4 ohms so good if it was short circuited or 

OL it would be faulty.

Next i check the high voltage output side tap of transformer you test for the terminal 

pin to ground and usually read from about 90-180 ohms and should not be short circuited 

This one reads 75.8 OHMS so happy with that 

next i test the secondary winding of transformer it can take some tracing which wire is 

which but you should find them , trace them back to the transformer and test this one reds 

1.3 ohms and is not short circuited or leaking to earth so good 

Next i switch meter to capacitance mode to test the capacitor and test across the 

DISCHARGED capacitor it reads just under  micro farad check side of capacitor to

see actual size to compare

Next i test the diode i cannot get  reading in both diode mode or high ohms 

im suspecting it might be a fail but you need to do further testing in order 

to be certain.

see video here for testing these 

as you can see i tested in both direction instead of swapping 

the clip around i just swapped leads in meter as its easier but just ensure you test both ways 

see video link to see a good reading 

if the primary side or transformer is not getting power it could be either 

micro switches or this rely on the main control board and is about the only repair that can be done on board before needing to replace the PCB

Part 2

The difference between cooker and an oven

Bit basic but surprising how many times i get sked this and if you do not know then you do not know so ill explain here 

A cooker is freestanding all in one type unit with at least one oven and hob on top, it stands as an individual appliance on the floor usually fitted in a gap left in the worktop surfaces of the kitchen. They range in size power and options but are an excellent compact appliances to suit most needs. And eliminate the need to purchase and fit multiple appliances.

An oven is just used for baking and roasting and is usually fitted into a bespoke integrated kitchen cupboard made especially for ovens and can be fitted at different height levels if needed.

Basic cooker / oven functions

Conventional convection cooking usually uses 2 elements one on the floor the oven on the top of oven , this creates heated convectional air currents that circulate around the oven cooking the food. The main draw back is that there can be pockets of cooler air within the oven and also it can take longer and also use more energy to cook 

Fan assisted ovens use a fan usually at the rear of the oven to circulate the heat from the element round the oven space with this type of oven shelf height does not greatly affect cooking times and temperature is more even distributed round the oven.

These types of oven typically use less energy to cook the food and can cook food in low times and at lower temps.

Grilling sometimes called broiling uses the top element and directly heats the food. Grilling can be done with the door open as it does not require the door to be sealed to aid the hot air convectional currents.

Grilling is very fast but can burn the surfaces and leave the middle uncooked if not controlled properly 

Pyrolytic cleaning an oven or cooker

Pyrolytic ovens are basically an automatic cleaning system , The system heats the inside of the oven until it reaches 400 degree C this turns any food residue to ash which can then be wiped away once the oven cools again and the door lock opens.

Due to the temps reaches during this cleaning ovens with this option usually have  lot more heat insulation around the outside of oven and also have more glass layers in the door.

The door is always locked during the operation and some ovens re fitted with catalytic convertors to filter out smells as well.

Remove everything inside the oven, close the oven door and select the pyrolytic cleaning function.

During pyrolytic cleaning, the internal temperature of the oven will reach 400 + °C.

The glass door of the oven might be hot to touch. Do not touch it during the cleaning cycle.

Once the pyrolytic cleaning is completed, you can wipe away any remaining residue inside the oven with a damp cloth.

Cooker oven timers - PCB - components testing

The cook timer can be used to turn the oven on at a certain time or to turn it off after a set duration, timers usually consist of an LCD screen display selection buttons for setting timing and clock , a PCB board with relays to do the switching and a audible buzzer to signal operator when timer has finished count down.

Some timers use the frequency of the mains supply to time the clock other use quartz crystal as in a digital watch this type are a lot more accurate.

When you set the time to turn on or off on these clocks, when the time is reach the PCB will operate a relay that will them control the element required.

Common issues with these include 

If you have no power to oven setting the time can solve this a lot of time i have been called out after a power cut only to i find the oven time has reset and oven will not operate.

Test for power coming into the PCB , check for any fuses as well. You can also test the relays or bypass them by removing the outlet side terminals and jumping them to see if the oven elements now operate.

Sometimes heat can damage a PCB board and timer will need replacing but you may need to look for the cause of heat it could be insulation loss a faulty thermostat or a missing and or damaged door seals.

PCB , Capacitors - MOV - Resistors - Diodes - Relay - Speaker - Transistors 

Testing electronic components with a multimeter ( Basics )

Testing basic electronic components, i use an electronics learning board to practice testing i recommend getting one if your a beginner here i show you some testing on the learning board and real components.

First ill start with resistances on the learning board here is a photo of all the resistances on this board from 100 ohms to 0.470 M ohms.

So set your meter up to read ohms on the selector dial and the leads in correct terminals.  

Connect across each resistor to take a reading .

First resistance i measure is 100 ohms the reading automatically reads 101.4 so close enough for me 

Ill do a few more measurements on resistances and on real resistance components 

Below 4.7K resistance

Below 470k or 0.470 M ohms 

Now ill do some real resistance components 

Next capacitors so i select capacitance on dial and them blue button to shift to capacitance mode 

First one i read is 3.3 micro farads 

Then a 0.1 micro farad 

and lastly a real 0.1 micro Farad capacitor 

Next ill test diodes you need to select diode mode on selector dial and this reads the voltage across the diode you need to test both ways one should give a voltage reading the other way should not allow current to flow and hence show OL on meter 

OL one way and 0.3v the other so a good diode 

Same below but on a real diode component

OL one way and 0.56v the other direction 

Now i test transistors you should get voltage one way but not the other similar to a diode as this is what a transistor is a combination of diodes.

You need to test from Base to Collector and Emitter with one lead and then reverse then you should similar to a diode get 2 OL reading and 2 voltage readings 

OL reading with red lead to Base and black to Collector 

Red to Base black to Emitter 

Now reverse leads black to Base and read to Collector  and 0.7v 

Black lead to Base and Red to Emitter 

Testing electronic components with a multimeter ( Basics )#

And below on a real transistor 

Here i am taking out a timer LCD display and PCB board out of a cooker unit its easy to do once you get into it..

Remove the buttons form the facia panel 

2 screws held the panel in place 

the panel in this model is screwed to the panel make sure you note the wiring 

or take photo

lots of components can be tested and replaced on the board or just replace board all together 

Cooker oven timer LCD PCB removal repair replacement video click to watch

Cooker Oven door locks

synchronous motor lock

When Pyrolytic cleaning an oven or cooker the temperatures inside the oven reach over 400 degree Celsius obviously these temperatures are very dangerous so the oven with automatically lock the door to prevent the door from being opened until the oven is cool enough to not be a danger.

There are a number of way the oven can automatically lock the door using either a wax actuating lock, synchronous motor locks or solenoid locks.

The wax actuator uses heat to expand wax within the lock this expansion pushes on an internal mechanism with pushes a pin to lock the door in the closed position, when the wax cools the pin will retract again and the door will be unlocked and able to open again.

Synchronous motors use the motor to turn the lock to the closed position when the motor receives the signal to do so, when the oven has cooled the motor will open the lock as well. There could be a microswitch as well to signal to oven PCB that lock is engaged or not , this should be tested for continuity as well to ensure its functioning.

Solenoid lock uses signals from the PCB to power the solenoid operated lock ,this also may have a microswitch to signal correct operation  of the mechanism, you can test the winding to ensure it has continuity and to ensure the correct resistance measurement.

Common problems

Can be caused by component failure or damage , this can also cause secondary damage for example if the lock stock open and the door slammed it could break door frame so inspect prior to replacing any components. You can test the motor and windings of solenoid valve and visually inspect for damage. 

Cooker oven - Heating elements

On ovens the heating element is basically a resistance this i what is found in an heating element even light bulb elements, the resistance to the flow of electricity creates heat.

Without a thermostat to control the element it would just continue to heat until the element eventually burned itself out.

The element its self is high-ish resistance metal ( nichrome ) this is surrounded by an electrical insulating material and finally a metal outer coating to protect the element.

Element can be fitted in the bottom or top of ovens or at the rear surrounding the fan, some can be dual elements and be grill and oven elements combines and other my have the capillary tube of the thermostat fitted to them too.

Elements are usually screwed to the inside of the oven cavity with 2 screws and the wire terminal are outside of the cooker at the rear, it is usually possible to change the element over without having to enter the rear cover by pulling the wires through into cavity.

When replacing the elements ensure the power rating and size of the element are taken note of as they do look similar but need to replaced like for like.

When testing the element its best to check for continuity with the ohms setting of a multimeter and if one is available you can insulation resistance test the element to ensure internal insulation is still insulating the element efficiently. Elements usually read around 20-30ohms 

Common faults

Over many years of heating and cooling the elements can become warped , damaged internally or even split open , this can open circuit the element or it can trip the RCD or MCB. Some times you can just look at the element and see the warping or splits easily but it may be necessary to test the element for continuity and or insulation resistance test the element to test for insulation breakdown.

On fan assisted ovens check the fan as well as sometimes fan failure can cause the element to overheat and fail so its always worth checking the fan assembly when fitting  new element.

Cooking and cooling fans - motor noise common issues and testing

The fan is used to circulate the air inside the oven cavity, this evens out the temperature all round the oven cavity , which id in the cooking process reduces heat and energy needed.

Commonly the motors used are shaded pole motors which are single phase AC induction motors simple but reliable motors.

Common issues

A visual inspection will show if grease or food or other materials build up inside the mechanism or other things getting caught up in the rotor blades can all be common issues, these can slow the motor down and even create overheating in the motor and eventual breakdown. 

To test the motor winding you will need to set your multimeter to ohms and test between the two motor winding terminals. 70-110 ohms is usually the range to expect , you can also test the motor winding to earth and insulation resistance test if required.

You can also do a visual inspection of the motor to look for damage or burning discolouring in the windings. 

Its always wise to spin the blades as well to make sure they are not rubbing or making contact to anything which will cause a lot of noise when the fan kicks in.

Cooling fans are used to cool the chassis of the oven so that any parts that are exposed to the touch are kept cool via cool air from the room and safe to touch. Cooling fans look different but the motors are usually the same type of shaded pole motor.

To test the motor winding you will need to set your multimeter to ohms and test between the two motor winding terminals. 80-150 ohms is usually the range to expect , you can also test the motor winding to earth and insulation resistance test if required. Visually inspect fan operation.

Cooker oven thermostats - operation, testing and common issues

The thermostat is very important part of an oven as they regulate the temperature inside the ovens cavity. The thermostat is part of the heat selector switch and detects heat within the cavity by means of a capillary tube.

When the oven heats up the gases inside the capillary tube expand this puts pressure on an electrical contact inside the thermostat as the heat rises eventually the expansion of these gases will open the electrical contacts turning off power to the heating element, the cavity will them begin to cool again and the gases in the capillary tube will contract again until the electrical contact makes contact again and turns the element back on. This cycling on and of of the element is what keeps the oven at the desired temperature.

The electrical connection point can be varied by adjusting the selector switch, if you select a higher heat setting then it will take longer for the expansion of the capillary gases to disconnect the element this means an higher temperature will be achieved as the element is kept on for longer. This allows some control of the temperature inside the oven to control if the cooking.

Common issues

Over time the thermostat can go out of tolerance so the temperature setting is different to the actual cavity temperature you can test this by measuring the temperature inside the cooker. This has do be done over a certain period of time usually over 4 heat cycles of the thermostat to ensure the thermostat is regulating temperature correctly and the temperature of the oven is stable. 

So set temperature meter up to take the oven temperature and watch the thermostat light go on and of 4 times while monitoring the temperature, if this is out by 10% of the selector temperature then the thermostat needs replacing ( Central oven temp test ).

When cold or at room temperature with the selector switch on the thermostat should have continuity and when off it will read open circuit see video below on how to do this in more detail.

Safety thermostats - thermal cut out and cut in devices - cooker ovens

In cookers or ovens you will find bi metallic thermal cut outs or cut ins, these are used to either cut power to elements for safety reasons in the event of the oven overheating or to cut in the power to a cooling fan to cool the outer services the door or the ovens handle for example.

A bi metallic switch works on the principle of the differing rates of expansion of 2 types of metals this creates movement of the metals and this movement is used to make or break the contact.

For example a cut on/off device used to turn the cooling fan on at a certain temperature would test open circuit or OL on multimeter at room temperature and the contacts would not make or measure continuity on the multimeter until a certain temperature had been reached these will cycle on and off curing the heating and cooling of the oven so these must be designed to reset on and off when needed.. Where as a thermal cut off would open read circuit OL on a multimeter at a certain temperature to turn of the heater element and this should then not turn on back on again and will need replacing -  after looking for other potential issues which could of caused the overheating problem ( thermostat maybe ).

Its obviously important to know which device you are testing.

Common issues

With constant heat cycling of ovens this will put pressure on all devices and wear and tear will occur , and the devices can fail in both open and closed positions. Some times the cooker oven may be turned off at the switch before the cooling fan has had a chance to turn on and this overheats the internal parts of cooker tripping the over heat thermal cut out and these must then be replaced both thermal cut out and thermostat, other times the thermostat or switch may not turn off the element creating an overheat which trips the thermal cut out or sometime the thermal cut outs just fail.

Cooker oven control , selector switches

Switches are used everyday and wear and tear will always take place over time, selector switches are single pole switches and can be anything from 3 to 12 position which enable the multifunction capability.

The switches uses a cam that rotates this moves spring load contacts, as the cam rotates form the user turning the selector different connections are made creating different electrical paths.

The ovens wiring are attached to the rear of the selector switches  the terminals used are called amp tags these must be tight if they are lose the create heat this can melt and warp the switches and cams.

The body and cam are made of plastic and the electric connections intentionally are made of brass.

Common issues

As with any switches wear and tear can affect the operation of the switches which can cause the switch to not be able to select or hold certain positions and will mean certain functions may no work as intended.

A worm cam can also affect the contact integrity this will cause the contacts to overheat and the switch can melt if left , this can usually be seen during a visual inspection of the switches

You can test the switches by connecting multimeter leads to the terminal of the switch and testing continuity during operation of the switches. Reading should be very low ohms 0.0ohms 

Sometimes the internal contacts can weld shut , this is usually caused by failure of the heating element creating a large circuit current at the moment of failure this will usually cause functions to operate without the switch being on after replacing the element , so ensure you test and visually inspect switches with multi meter after fitting new parts if problems occur.

Cooker Oven PCB and Sensors , operation testing and common issues

In more modern ovens a PCB, Relays and sensors do the job of many of the selector switches, This enables very precise and economic control of the cavity heating saving energy and giving  better user experience.

Some of the less expensive parts can be easily tested and replaced on PCBs  but the more complex chips are not so easy to test find or replace and sometime its better to replace the PCB or it might be more cost effective to buy a replacement cooker oven depending on age of machine.

Some even give error codes it an attempt to help the engineer fault find but if the PCB is dead then this is not possible if you get error codes you will need manufacturer information to find the codes and solutions.

Common issues

PCB have many components and these can fail over time , it is possible for a failure in an oven component for example a shorted element or sensor to destroy board components so bare this in mind when doing your diagnostics on the machine.

A general rule is that if after testing all other components and eliminating them from diagnosis , and they all test good, then you can assume the PCB is faulty, this is an expensive call so you need to be sure.

Sensor are use to give the PCB accurate temperature measurements of the oven cavity to ensure precise cooking , these are usually NTC type temp sensors 

There are other methods to regulate the temperature but the most used today is the NTC sensor, the NTC sensor is a semi conductor and as the temperature in the oven cavity rises the resistance through the sensor decreases which is then used to control the on / off time cycling of the heating element.

NTC sensors monitor the cavity temperature and use this information to calculate if the heating time should be increased or decreased.

To test the sensor you need to set multimeter to ohms and check measurements against manufacturer documents. 

Its best to test the ntc at room temperature and measure against known good values but its possible to use hot water to test at a range of temperatures.

rough guide

20 degrees    expect  6050 ohms

60 degrees    expect  1250 ohms

80 degrees    expect  640 ohms

Common issues

NTC can fail open circuit as well so will test OL on the multimeter so test for this , it may also trigger an error message depending on age and make - model.

if they test OL  or out of specification then replace them 