Tumble Dryer Thermostats
When you are looking for a tumble dryer thermostat the first thing to do is, as usual, make sure that you have the correct model number of your tumble dryer and, in some cases you may need the production or serial number to ensure that you get the correct thermostat or thermostat kit.
Like almost all tumble dryer spare parts spares are identified by model number and production information, not by make, size or the various numbers that you might find printed on the thermostat itself, these are usually of little or no use.
After that, you need to decide (if the thermostats don't come as a kit or part of the heating element) exactly which thermostat that you need.
If you are not sure then either call in a professional tumble dryer engineer (see below) or use search function in the help forums for more specific information but you will still need model information to do that and, if you cannot get a result there please post your questions there for more help.
Almost all commonly used tumble dryer thermostats are available in the store.
Testing Tumble Dryer Thermostats
Here's a quick video showing you how to test most types of common tumble dryer thermostats but do take time to read the informatino below for a far greater understanding.
Tumble Dryer Thermostat Types
Essentially there are usually either two or three thermostats used on most tumble dryers however it should be noted that on newer models we have increasingly been seeing a move away from more traditional electro-mechanical thermostats to digital sensors or thermistors. Generally though any overheat thermostat or safety thermostat will be electro-mechanical, so far.
Most tumble dryers will have one or possibly two control thermostats depending on the design. All should have an overheat thermostat fitted for safety in case the tumble dryer should overheat and this one will cut power to the heater or the whole tumble dryer. And a few tumble dryers will have an exhaust thermostat fitted.
Whatever you do, do not live test the tumble dryer, all testing described here can be done safely with the tumble dryer unplugged from the mains supply.
Tumble Dryer Control Thermostat
A control thermostat will be the one mounted on or very close to the heater that controls the heating from the heating element in the tumble dryer. This thermostat is, if you like, the main workhorse when it comes to temperature regulation in the dryer as it will switch the heating element on and off as required to maintain the selected temperature or, in the case of a thermistor or digital sensor, will report back to the electronic controller to operate the heating element.
In most cases for an electro-mechanical thermostat it is in effect no more than a simple switch, switching on and off the mains live supply to the heating element.
Due to that the normal position will be closed, so a simple check with a multimeter will often reveal a faulty thermostat if it is open circuit when cold.
There is never any call to test these components in a live environment while mains power is on.
There are cases on some two heat tumble dryers where two thermostats might be used, one for the low heat setting nd one for the high heat setting. These operate exactly as described above and are tested in exactly the same manner.
Tumble Dryer Overheat Thermostat
The overheat thermostat is a safety device in effect. It is designed to cut the power to either the heating element or the entire tumble dryer if it is activated. Normally this would be a case of breaking the live supply to the heater or dryer thereby preventing further heat and, the possibility of a fire by shutting down the dryer's ability to generate further heat when it gets too hot.
These thermostats are normally closed allowing the circuit to be completed and the tumble dryer to operate and, when faulty or tripped, be open circuit. Again, these can be diagnosed quickly and easily with a multimeter and without any mains power being required at all.
These thermostats will usually come in three possible flavours, a self-resetting thermostat that, when it cools off will reset back to the default (normally closed) position allowing power once more to operate the tumble dryer.
The most common next type of tumble dryer overheat thermostat are the non-resetting kind which are most common in the Hotpoint and Indesit tumble dryers. This type of thermostat does not and will not reset, it is known commonly as a one-shot device, that is to say that, if activated it cuts the dryer or dryer heating element out and must be replaced before the tumble dryer wil operate normally once more.
The third kind which is common on White Knight or Crosslee produced tumble dryers is the push button reset type of thermostat. There will be a small (usually red) button on the thermostat that, when pressed, resets the thermostat and it will then operate normally.
Tumble Dryer Exhaust Vent Thermostat
These are much less common and generally only seem on older tumble dryer models.
This is a thermostat, very similar to a control thermostat mounted in the vent pipe of the tumble dryer and operates as well as tested in the same manner.
Tumble Dryer Thermistors
A thermistor can be used in place of any of these types of thermostats bar the overheat as they are basically just sensing the temperature of the air. The reason that these and other electronic sensors are being employed in modern tumble dryers is that they are more accurate at determining the correct temperature has been reached and can maintain a more stable and, accurate, operating temperature.
An electro-mechanical thermostat would typically have a range of around plus or minus 10-15% on the set temperature, even for those that only have one or two preset temperatures to operate to whereas a digital thermistor or sensor will be more like plus or minus 2-5% which, when you are trying to conserve energy, is a lot better. The prices of these components has also dropped considerably in the past few years allowing their use even on cheaper tumble dryers, even if they are not of such high quality or accuracy.
Like all thermistors there are two basic kinds, an NTC and a PTC. Normally, in this industry, it is an NTC type . if the resistance rises as the temperature increases it is a positive temperature coefficient (PTC) thermistor, or posistor. If it is an NTC type then the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor.
To diagnose whether a thermistor is faulty all that is required is a mug of hot water and a mutlimeter.
To test simple set your multimeter to read ohms (Ω) and read the thermistor's resistance value. There should only be two connections that you have so this is really easy an almost impossible to get wrong. Now sit the sensor end of the thermistor in the hot water and read the value there. If the value changes then in all probability there is no fault with the thermistor but, if it remains the same then it is almost certainly faulty.
Tumble Dryer Heater Assemblies With Thermostats Pre-fitted
This has become commonplace in the industry and, probably like you if you have one of these types, we often don't understand why you cannot buy just the dryer thermostats either.
Models have been on the rise with complete heater units that come with the thermostats pre-fitted and these thermostats are often not available as separate spares, you are forced to buy the complete unit to replace what should be a small thermostat costing a few pounds. It is completely crazy on many levels.
Except for one.
It is cheaper for production to supply "units" and just like some spares for washing machines, cookers, dishwashers and most other appliances it's all about costs as retailers and consumers want appliances that are cheaper and cheaper to buy in the first place, the problem is that often means you get stung further down the road.
But we move away from the point, the point is that there are tumble dryer heater element units complete with thermostats out there and we (nor anyone else) can get the thermostats separately as they are simply completely unavailable. Your only choice is to replace the complete heating unit.
Why Tumble Dryer Thermostats Fail
It is worth pointing out here the number one, top reason for tumble dryer thermostats failing is people not using the dryer correctly!
All modern dryers need to cool off before you open the door, even for a few seconds, as this allows the heat to build up in the heater area and will very often pop the overheat thermostat. Now, as engineers we don't mind that as it's a nice easy repair for us and, as a spares seller we don't mind as people buy lots of thermostats from us but really, we'd rather you didn't have to for such a silly reason.
Let the dryer cool off before you open the door and do not open the door to "check if it's done" before the last ten minutes has counted down.
If you ignore us that's fine, but you'll probably be needing our services should you ignore this advice.
The second top reason is that people fail to clean the filter and condenser chamber on condenser tumble dryers. Usually we are met with a "I always clean it" but the evidence inside the machine tells a different story and, people forget to do it as often as they should. Which is why manufacturer's put warnings and labels on tumble dryers telling you to clear the filter after every use, they don't put them there for fun, there is a reason and a good one.
If you kill the airflow, you will kill the dryer. It's that simple.
Further Tumble Dryer Help
If you need more help please feel free to browse the self help section of the site where that are other articles to help you diagnose common tumble dryer faults and, if required, use the forums.
For tumble dryer spares please use our online spares store and, should you have any difficulty finding the thermostat you need, simply contact us from that link or from the form below.