Heating and Water not Switching Off

[j501]

I have a Honeywell 94000C Controller but when I turn either water or heating off, the boiler does not respond. The lights go off on the controller and the remote thermostat turns off so I am assuming the controller is OK. Likewise this is a new controller and the same fault existed with the old one (hence the replacement)

Any ideas?

 

[stem]

By "not responding" I assume you mean it doesn't switch off, but keeps running.

If you have a motorised valve (or valves) the boiler is switched on and off by a microswitch inside the valve head. They can stick in the 'on' position and cause the symptoms you describe.

It there has been a short circuit, sometimes it's possible to weld together the contacts inside the programmer, however this is less likely than failure of the microswitch