Hotpoint (Whirlpool) TDWSF83BEP Door Filter Light?

Hi Everyone

Im looking for a little assistance into a tumble dryer fault please. The door filter light comes on, if you push start it comes back on again but then soon cuts out again with the red light on. So i have investigated and the following has been done.

Tumble dryer does get warm but keeps cutting out with red door light.

I dismantled door filter and cleaned any lint debris from filter and duct, almost none but a little.
I removed condenser and cleaned under tap as per instructions found on line.
I removed right side of machine and found lint under the sensor by fan motor, removed this as thought this was problem, but machine still does the same.
Opened covering here as well and cleaned any lint from here, only minor.
Removed rear heater to look to see if heater had any lint, but hardly any found.

Now starting to struggle :-(

So tested the NTC sensor on top of heater and the thermal fuse, thermal fuse has continuity and sensor has resistance circa 18k Ohm that reduces when warmed.

tested sensor by fan motor (NTC?) and again this has a resistance and reduces with warmth.

So I inserted a thermocouple close to the two sensors at top of heater to see what was going on and when you start machine it appears to turn heater on which rises to circa 250 Deg C this then reduces down to circa 30 Deg as fan blows air through. It tries again to heat and it goes to circa 340 Deg C but then stops and lights the door filter light.

Removed and reinstalled connections to pcb by selection knob but no different.

I guess the thing is cutting out because it thinks blocked by lint and overheating but sensors appear to be ok, can anyone help with spot where my thoughts are wrong please?

I would like to know how this system works, is the machine supposed to regulate the power to the heater depending on temperature or is it just a relay or some switching transistor that crudely switches on / off to control temperature and thus the speed of response of the sensor is also important.

So I removed the NTC sensor above heater which is as follows:-

Manufacturer ELTH (that's interesting as they make stuff for us at work in the fuel injection industry).
Type 279
T200
Date 11/15
Designation? 3111

Set up was in our lab at work in the test oven with wires soldered to spade terminals, results as follows:-

25°C 12.4K
60°C 3.2K
70°C 2.4K
95°C 1.5K
100°C 1.05K
110­°C 0.82K
130°C 0.6K
180°C 0.27K

Test lead resistance 0.020K (insignificant)

Anyone know the specs and tolerance for this device? I can find some details on line for a whirlpool machine but it doesn't state the type of NTC this suggests at 180°C it should be 0.1K, now normal resistors have tolerances circa 5% and this would be way out, but on an NTC i have no idea, anyone?

Specs found online for a whirlpool device

25°C 12.0K
60°C 3.0K
70°C 2.2K
95°C 0.1K (although this looks suspect value in manual)
100°C 0.8K
110­°C 0.6K
130°C 0.4K
180°C 0.1K

My values seem shifted by circa 200 Ohms but this may be down to my device not being the one quoted in the whirlpool manual??

Thanks

Kevin

Kevin
March 2017