Webasto Thermotop c refuses to switch off

[Rhe man]

Hi

My Thermotop C will not switch off. Only way to stop it is to remove the red 20A fuse.

Runs normally with out a problem.

Rang Webasto, no help, never heard of  this.

Any one had this problem and could help.

Disconnecting the timer will not switch it off either

[TheBiscuits]

How long does it run for after you switch it off on the controller?

[system 4-50]

How long have you had it?

Has it always done this?  If no, what else has (been) changed ?

 

[Tracy D'arth]

Are you sure its not just the automatic cool down period?

 

If it is continuing for ever, it must be getting a live feed from somewhere it shouldn't.

[Rhe man]

First thing to happen when timer is switched off is for the pump to stop. If I disconnect the punp then it will shut down, try to restart then  go int  lockout. ??

Heater is 15 yrs old, never had a problem. Nothing changed. very occasionally it will shut down normally.

[Chewbacka]

Corrosion or loose strands in a connector bridging the trigger wire to +12v wire?

[Rhe man]

Will run until I remove the  20A fuse, no other means of stopping it unless I disconnect the  fuel pump. Looks like the control unit as that's where the off signal 0V goes to.

[Rhe man]

Only main 12v supply at 20a fuse. stays on whether heater is on or off as it is supposed to do.

Perhaps a glow pin/flame sensor fault?

[Sea Dog]

1 hour ago, Rhe man said:

Heater is 15 yrs old, never had a problem. Nothing changed.

Erm, if I may, something definitely has!

 

[Tracy D'arth]

Am I right in thinking that the T/top C has a relay inside? If so it may be that the contacts have welded together.

Edited December 15, 2020 by Tracy D'arth
added news item as requested.

[Rhe man]

More investigation today

 The heater DOES sut down but after 10 secs restarts. disconnect pump and heater will run combustion pump and water pump continuously.

 

Again only way to stop it is to disconnect  12v to 20 A fuse.

It fires up as normal and modulates as expected.

 

Stops instantly when the 12v supply is removed. Will start as normal straight away,

[Detling]

Sounds like something 'connecting' the start signal line to 12 volts. could be a poor connection strand bridging terminals, somewhere the wire has been trapped or has chafed and the two cores are connected inside the wire, moisture on a set of terminals, you need to disconnect the trigger/stert wire at the webasto control board and fit a small short pair of wires in their place, touch the ends together to start it and then when running fully open them and see if it stops after it's shut down routing which is several minutes long. .

[Sea Dog]

I've a feeling this one is just gonna run and run...