Hi, Can anyone help please. I have a white knight WK447 tumble dryer which is about 7 years old. It is working fine but has now got no heat. The filter is clean and free of lint, the dryer has not been moved or disturbed from the position it has operated successfully from. The only thing I have discovered that could have made a difference is that two of the three flaps on the exterior air vent had got stuck because the building has just been painted. I have pressed the reset button on the back of the machine whilst it was operating but it is still cold. I have looked on the internet for parts and I think it may be something called a thermostat exhaust but I'm not sure and have no idea where it is in the machine or if it is possible to replace it myself. Many thanks, Pam

There is normally a high-temperature switch mounted to the back of the tumbler, which drops out the heater contactor, when it senses a high temperature (or fails). Running with a restricted discharge vent will cause this.

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Originally Posted by rsain2004

There is normally a high-temperature switch mounted to the back of the tumbler, which drops out the heater contactor, when it senses a high temperature (or fails). Running with a restricted discharge vent will cause this.

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Hi, Many thanks for your prompt reply. The high temperature switch that you mention is the red button that I pressed. It says in my manual that it will click if it has been activated but it didn't make any noise when I pressed it to reset it and after 15 minutes it was still cold.

Most probably the dryer overheated.
As it is not the high-temperature switch, open the rear panel and check if the heater element is perhaps burned out.
You will need a multi-meter (and know how to use it). Disconnect all power form the dryer : put the mains cable in front of you on the ground. Disconnect one of the heater element wires. Measure the element on resistance. Should be around 20 Ohm. If you do not measure any resistance, the heater element has burned out and has to be replaced.

Success!

Many thanks for your reply. We have opened the back and looked inside and nothing appears to be burned out. My husband is talking about buying a multi tester and having a go at using it. What I don't understand is why the safety cut out switch didn't work and why the machine overheated and tripped the electrics. Also, having looked at the inside of the safety cut out switch I can't see what it is meant to do. It barely shows any signs of moving or doing anything. Pam

Dear bigbertha

A simple multi tester will cost you around $ 10-15.
As to the safety cut out switch : may be that caused the problem in the first place.
So check that one electrically too! Most such switches function by a slow process that is based on thermal expansion, resulting in a cut-out of the heater power. When cooled down they look "normal" again. May be this one is not sensitive enough.

But that is not the cause of the lack of heating : so check the heater element first, and make sure the fan is blowing all the time the heater is "on". Do that all with the power cord disconnected from the wall outlet.

Danger : be very careful to measure anything with the power connected. Always have a second person next to the power cord to unplug it in case of shock.

When everything seems OK again, and it still is not heating, than switch your multi meter to AC high voltage and measure on the contacts of the heater element for voltage. If there is no power follow the wiring to find the cause of the power interruption.

Success !

Thank you for all you help and advice. I will keep you posted as to how we get on. Pam

Hi, thought I'd update you. My husband bought a multitester and tested both elements and they both gave readings so we assume they are both working. He also found two thermostats, one of which is the control thermostat and the other is the exhaust thermostat and tested them both and they both registered 0 when it was set to Rx1. We think this means they are also both working. The machine still works but still has no heat so it looks as though we may need to pay to have it looked at as we don't know what else to do now. Any suggestions. Thanks again. Pam

The relay that turns the motor on, is generally different from the relay that turns on the heater... perhaps the heater relay has failed...

Hi, thanks for your reply. You may well be right but I have no idea what a relay is or where to find it or how to test it. I don't suppose you can help can you?

A relay is essentially an electric-powered switch. There are many different types. You can find it by following the wiring at the heater, back to the next device. In most cases, the wiring from the relay-controlled device leads from the device to the relay. At the relay, smaller-sized wires will lead to the device that controls the relay... a timer, programmable controller or something like that, which should also be inspected...

Please be safe...

Many thanks again. If nothing else I'm learning a lot. My husband (who is very grateful for the advice) will check in out tomorrow if he can find it and work out how to test it with a multitester. Pam