Baxi Megaflo 24HE boiler Central Heating constantly ON

[Coffee_drinker]

Baxi Megaflo 24HE boiler
Unventend system
Danfoss FP715-Si programmer
Danfoss manual room thermostat

Few months ago switched from Vented to Unvented. All worked perfectly until few days ago.

Couple of days ago Central Heating came ON and it stays ever since. Room thermostat is turned down to Min, Programmer is in CH OFF position. Checked the wiring on both and even removed both programmer and room stat from wires and Boiler still fires and CH comes ON. Weird.
In oder to have Hot Water, I need to manually turn the programmer to ON and then boiler heats the HW tank. When I switch HW off, CH comes on and it stays ON. The only way to turn it off is to Turn Off whole boiler (even Reset button on the boiler does not work).

Any ideas??

 

[flameport]

Motorised valve stuck open, or switch inside it has failed in the on position.

 

[Coffee_drinker]

Thanks flameport -- I check the valve: all seems OK (it's new from the installation last few months).
I opened the pcb and ckecked the switch - again nothing unusual. How can I check that the switch has failed?

 

[Hason]

Get your electrician to check switch live/heating wires in wiring centre if you have an rf stat it may be sending voltage back even in off position,due to the relay in reciver.

 

[Coffee_drinker]

thanks Hason - will do.
I will post back results