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Most thermostats that you see in a fridge, freezer or fridge freezers are electro-mechanical in operation although, in recent years with the advent of electronic controls creeping slowly into the domestic refrigeration market, electronic sensors known as thermistors have become more commonplace.

The older method remains popular, especially so on many low cost refrigeration units simply because they are generally cheap, simple and usually fairly robust. They are therefore extremely common.

Diagnosing a problem with a simple thermostat is not that hard, even for the inexperienced as, although many people think that these simple components are more complex than they really are, they are merely a simple on and off switch regulated by temperature.

  How Thermostats Work

There is more in this article on how fridge and freezer thermostats work but, the short version is that in the phial as shown in the image below, there is a gas held.

Diagram explaining a fridge or freezer thermostat

The phial is normally attached to the back wall of the fridge or fridge section in a fridge freezer directly onto or where the evaporator (the bit that cools) is mounted on the wall or behind it.

The gas in the phial then expands and contracts causing the switch in the thermostat body to be operated switching the unit on and off.

This is known as cycling because the thermostat "cycles" on and off in a temperature range.

It should be noted that temperatures can vary here and that it is perfectly acceptable, on a domestic unit at least that isn't being used for special purposes such as medical use, to be something like +2˚C to +7˚C giving a mean of about +5˚C and the deviation can be greater than that at times. The trick here is to remember that this is about the mean temperature, not the extremes.

Inside the thermostat body will normally look something like this:

Inside of a fridge or freezer thermostat and how it works

In our experience on virtually all domestic refrigeration you will see the first kind, the toggle type.

As you can see though, from a servicing point of view this is a very simple device.

  Known Thermostat Faults

Almost all electro-mechanical thermostats have two states. On and off.

It is extremely rare to see anything other than that in terms of status in a domestic refrigerator, freezer or fridge freezer. Electronically controlled models are of course completely different and different principles apply but for the older types, dead simple stuff really.

So when a thermostat goes faulty you will either get the unit running all the time or, not at all.

Here's the easy part, if the unit is running all the time and your fridge or, fridge section of a fridge freezer is freezing everything in it then the odds are it is merely a simple thermostat fault.

Replacing the thermostat will cure that fault in almost all cases.

There are other faults that can cause this or, symptoms like this but they are far rarer than a stat fault.

If however the refrigerator or freezer is not running at all then there are a number of other things that can fail and cause that to happen, you can't guarantee that the thermostat is faulty. This isn't so common on fridge and fridge freezer thermostats as usually when they fail they tend to fail closed, so the machine runs constantly however it can and does happen that the thermostat fails open and the machine appears dead.

  Temperature Ranges And Cheap Thermostats

There are some sources on the internet that say you can fit any old thermostat to almost any fridge, freezer or fridge freezer. These would usually be the sites that are selling the bog standard universal thermostats for a few pounds, often the cheapest ones you can get.

It isn't true.

As with most things, if it seems to be too good to be true, it probably is.

A lot of thermostats are designed with particular phial lengths or temperature ranges depending on where they are placed within the cabinet and fitting the wrong one can lead to disastrous results.

Your fridge may not cut in at all and not cool or, it may never cut out and freeze everything.

Getting a correct suitable replacement thermostat is essential and, if you don't know what you're doing or looking at, that's going to be pretty hard. So, for a novice, think, impossible.

A lot of the really cheap fridge and freezer thermostats we see smack us with "cheap and nasty" as soon as we see them. We don't sell those, they're cheap and nasty with the emphasis firmly on "nasty".

Do keep in mind that you are relying on this little device to keep your food fresh and safe so that you don't get a dose of e-coli, salmonella, listeria and other nasty stuff.

According to research a fridge salad drawer contains 750 times the level of bacteria that is considered to be safe, you don't want to be adding to it by trying to save a couple of pounds on a replacement thermostat.

  OEM Only Thermostats

There are a number of thermostats for all fridges and fridge freezers more than for freezers that are what we call OEM only, that is to say that a replacement thermostat will only be available from the Original Equipment Manufacturer and there is no alternative.

We see a lot of these on integrated fridges and freezers as well as more specialist models, especially those with multiple temperature zones.

These tend to be more expensive, sometimes a lot more expensive but, the positive is that they will fit easily and operate as they should.

If we advise you can only use the OEM thermostat, we pretty much know that will be your only option and whilst you might be able to bodge something up with a cheap thermostat, it probably won't work properly or fit well, if at all.

More on fridge thermostats can be found here

M ICHAEL JOHN MARSDEN
servis u/counter fridge freezing
can you supply component and provide fitting instructions ?
M ICHAEL JOHN MARSDEN
SERVIS U/counter fridge freezing everything even set at 1
Can you supply a new thermostat ( if that is the problem) and show how to fit
lola
Bosch Fride Freezer MY BOSCH FRIDGE DOES NOT COOL AND THE ALARM IS CONSTANTLY ON
MY BOSCH FRIDGE DOES NOT COOL AND THE ALARM IS CONSTANTLY ON.
ENR - KGU32123GB/01

Terry
Schreiber apm 6314 integrated fridge
My fridge has stopped working it does not cool anymore the only thing that appears to be working is the light inside ?
Lizzie
Bush fridge freezer
I bought a bush fridge freezer a few months ago. the fridge works fine but the freezer doesn\'t seem to freeze properly. Occasionally some bits stay frozen but then things like ice cream just melt. Do you know what it would be? I\'ve looked for a temperature adjustment but I can\'t find anything
russells5
Faulty Hotpoint Fridge Freezer
Hi - I have a Hotpoint RFAA52S fridge freezer which has just started playing up.
No matter what setting I put the thermostat on the Fridge is not working at all - freezer seems to be working and then stops freezing and ice melts and then goes cold again - but not as cold as I would expect. The light in the fridge works - its making a \"running\" noise.
Does this sound like a thermostat problem - which I\'m confident I can replace myself - or does this sound more complicated involving an engineer call out , in which case I might just buy a new one.

thanks

martin
husquana freezer
I have a Husqvarna freezer where with the main switch on the motor doesn\'t cut off but freezes to the maximum
30 degrees minus.
Ideas please to recitfy.

Kenneth
Hi Martin,

Sounds like the thermostat has failed, you will need to replace it I expect.

martin
thermostat on husquana freezer
Thank you Kenneth.
Yes assumed this might be the problem.
Can you tell me please where I could buy this from and is it easy to fit?
Alternatively do you have or know of any engineers in my area who could change this for me and what sort of cost would it be?
Thank you and I shall look for your reply.

Kenneth
For a Husqvarna machine you will struggle to get a direct replacement, if that\'s even possible but you should be able to use one of the universal ones from the following link, just working out which one can be a challenge at times.

Universal fridge and freezer thermostats

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