Heating problem

[Go4t]

Hi, my heating system has developed a problem where I can turn the heating or hot water on/off via the relevant t/stat with the programmer set to off or timer setting (once/timed). When it comes on via the timer it works fine.
The room stat and programmer were replaced about 3yrs ago and the mpv about 6 months ago (all like for like)
I'm thinking programmer but just at a bit of a loss with it at the mo. Any advice or pointers would be greatly appreciated.
Drayton room stat RTS1
Drayton cylinder stat HTS3
Drayton programmer LP522
Drayton mid position valve MA1
Ideal Mexico 2 boiler
Grundfos selectric pump

Cheers

 

[D_Hailsham]

So you can turn the boiler on, even when the programmer is OFF, by turning the CH or HW thermostat up?

This sounds like a programmer fault, but it could also be the valve.

How a mid-position valve works does what it says on the tin and also has detailed fault finding instructions. It will also save me time giving you the instructions.

Come back to this topic if you have any problems/queries.