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  Fridge Freezer Thermistors

On modern electronically controlled fridge freezers you will find that, instead of an old analogue thermostat that we now have small digital temperature sensors known as thermistors. These electronic sensors are also widely being used in other appliances as well now notably in washing machines but we are seeing them increasingly used in tumble dryers and cookers as well.

Thermistors come in two basic flavours, NTC and PTC.

If the resistance rises with increasing temperature then the device is called a positive temperature coefficient (PTC) thermistor, or posistor. If the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor.

Resistors that are not thermistors are designed to have a resistance as close to zero as possible, so that their resistance remains nearly constant over a wide temperature range.

Where appliances are concerned the most commonly used type appears to be an NTC and they commonly referred to being such in the industry.

The reason for using these devices is very simple, they are cheaper and more accurate than old analogue thermostats and allow far greater control as they read a range of temperatures as opposed to specific preset ones found on older thermostats.

  Thermistor Reliability & How To Test

It is worth noting that while on some appliances that these fail rather regularly, such as in the Hotpoint Mistral fridge freezer range, they are for the most part a pretty reliable device in our experience.

We are often asked to supply these when we pretty much know that they won't be faulty.

Thankfully they are easy to check to see if they are faulty.

Normally thermistors used in appliances are measuring temperature and reporting that back to the electronic controller as a value k? (kilohms). The value of resistance can be easily measured using a common multimeter set to the correct range and that will display the current resistance.

It should be noted that the resistance values can vary widely from appliance to appliance and it is therefore not possible to tell you what value you should be looking for generally. In fact, in many cases even in the "service" information we get as engineers we don't get the values either.

However, that doesn't really matter in many ways when proving if a thermistor is faulty or not.

With the multimeter connected and showing a resistance value you can then change the temperature of the thermistor by cupping it in your hand or placing it near a cool or hot source, which is another reason to give the engineer a nice cup of tea as it's ideal to hold the tip of the thermistor against the outside (safely of course) and watch on the multimeter for any changes in resistance.

If the resistance changes, chances are that the thermistor is good. This obviously isn't always the case but 99% of the time this will be true.

If the resistance does not change, chances are the thermistor is faulty. Again, obviously not always the case but it will be almost all the time.

Although this is a quick and dirty way of testing a thermistor, it works and it's fast.

  Fridge And Freezer Electronic Controllers

If most refrigeration that uses thermistors, some notable exceptions excluded, it is much, much more likely that the electronic control card has failed rather than the thermistor but there are a few things to check before you swap that out.

Make sure that the connections are good and clean on the board as, if they are not, this can cause all sorts of strange errors. Remember that as the controller read resistances anything that can alter that reading by the electronics will cause a problem.

If you can, reset the card totally.

Make sure that there is nothing touching the thermistor that could cause a false reading or that could be blocking a proper reading.

Defrost the fridge freezer completely and restart it, even a frost free one as ice build ups can cause the sensors to read incorrect values, especially in a freezer.

If all that's okay and the thermistor tests out okay, chances are the board is faulty.

Control boards and Thermistors for the most popular applications are available in our online shop and, if you can't find what you're after then please just ask us.

As ever, if you cannot use a multimeter of if you're not sure get a professional to look at the machine for you.

As with all electrical appliances, if you are unsure then DO NOT attempt a repair yourself. you could injure yourself or anyone that uses the appliance!
Christopher felix
Fridge freezer
Hi, I've got this fridge freezer by John Lewis, it goes on and off within second and I was wondering what the problem could be. I read some comments on your web site that it could be the thermistor. It's digital temperature. Unfortunately I tried to locate where it is to no avail. Kindly help please.



david graves
Both the fridge and the freezer have started operating far too cold. Fridge at minus 15 and freezer at minus 30. I have replaced both control boards, and still no joy. What is my next step? Suggestions most welcome. Regards Dave.
david thain
lec fridge freezer
i have an LEC T2855W fridge freezer.freezer section works fine but fridge section freezes everything LEC no longer supply thermisters for this model is there another one that could be made to fit or could it be another fault any help would be appreciated
Hi did you solve your problem as my fridge is doing exactly the same and I\'m having trouble getting it repaired Thank you
BEKO Fridge FReezer CDA543FW-2
I have a Beko fridge freezer CDA543FW-2.
It was recently moved between rooms and restarted after 24hrs.
The freezer is working normally.
Everything in the fridge compartment is freezing also.
I have researched forums and the consensus is it is either

1, Sensor built into rear lining of fridge which is NOT a replaceable part.
2, The main PCB control Board at approx cost £27 to £30

Is there any way of testing which is at fault OR could it be something else?

Any help would be greatly appreciated.


James Melvin
Freezer temperature
Hi, I have a Whirlpool American style fridge freezer 8586 162 15000, fridge is fine, freezer is not getting cold enough, it freezes water but not ice cream. I get error code of -- confirming issue with freezer temperature also occasional alarm. tried switching off etc. With the door open, if I press the door closed button the fan/blower comes on blowing cold air, there is no ice build up. Is this likely to be the Thermistor, if so where is it. I have electrical training.
Thanks guys

H James,

You will really need to use the forum for diagnostic help with a problem like that.

Hotpoint Mistral - we have had a Mistral Fridge freezer for some considerable years. Over that time, I have had changed the yellow thermistor three times to repair the common issue of working freezer and warm fridge. In fact, last time I used a couple of 99p thermisters from Maplins and that seems to have worked extremely well. However, I now have a problem with the Freezer. Initially, I thought it was the yellow unit again as the fridge went up to over 20 degrees. I placed the freezer on FF to see if it was blowing the cold air into the fridge and after that cancelled itself after 48 hours, I noticed the Fridge went back down to 2 degrees. However, the Freezer is now showing - 31 degrees and seems to be working constantly. Will this now be the green thermistor. If so, do I remember correctly in that it is located near the yellow one? And finally, does anyone know the correct resistance reading so that I can repeat the act of replacing them with the actually component instead of paying the inflated price for the Hotpoint spare?
Ricky Cairns
did you ever get this sorted, i am having the same issue today
i have fridgefreezer but the fidge isnt cooling enogh can you help

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