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Bryan, Home Appliance Technician
Category: UK Appliance
Satisfied Customers: 12156
Experience:  EPA Certified HVAC
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Hiya. Bosch Exxcel Tumble Dryer WTA4107GB/01. Doesnt heat

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Hiya. Bosch Exxcel Tumble Dryer WTA4107GB/01. Doesn't heat properly, seems to cut out a lot so load doesn't really get warmed up and takes ages to dry, if at all. Voltmeter across heating element reads 235v on and off but only for short periods of time. I have checked all three control thermostats by the simple means of bypassing them but it doesn't seem to make any difference. I can hear something clicking as the heat comes on and off. Is there another thermostat somewhere which I'm missing or is there one built into the heating element? Element resistance is 20.7 Ohms. Is this what's failing?
Can you try something ? remove the vent completely from the dryer. run a load, Does it heat up fully then ?
Customer: replied 3 years ago.

I have already removed the dryer from it's normal site so it is sitting on the floor in the middle of the room with no vent hose attached. It still doesn't heat properly.

How strong is the airflow out of the back ?is it real strong ?
Customer: replied 3 years ago.

It's pretty good, not really strong tho'.

Okay, this should be flowing really strong out of the vent. If its not strong the thermistor will shut the heat down . I cant find the diagrams for this however. can you take the dryer apart and clean inside ? the blower assembly is most likely clogged.
Customer: replied 3 years ago.

I'll give it a go and let you know.

okay check for lint blocking the airflow.
Customer: replied 3 years ago.

Just took the back off and ran it (disconnected heater first!) and blower assembly is cleanseems to run fine. I ought to have said that a few months ago the overheat thermostat (with the red button) kept tripping. I took the machine apart and cleaned out all the internal ducts (I think it's 5-6 years old!) and it seemed ok then until this problem occurred. When it first happened I immediately went to reset it but the thermostat hadn't tripped. I also checked the thermostats and they do trip when heat is applied. Do you think something may have been damaged due to the previous overheating thing.

You may be on to something there . can you run this and determine if that clicking you hear is comming from the control board ? Bosch Control Module, Wta 3500 UC/04-10 (see 481590 for Uc/ 265677 from
Customer: replied 3 years ago.

Right, tried that. The control board isn't identical to your pic but similar and mounted on the RHS of the casing back a bit from the switch assembly. That right? Anyway, when I ran it this time it was clicking like mad and the voltage across the element was jumping around a bit until it finally went to zero, as usual. May be on to something here!

okay thats the issue then. the board is bad (the heat relay on it isn't holding in) you will need to replace the board. good job ! thanks , Bryan
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