Sticking motorised valve?

[cotswolds]

Hi all

There's a problem with the central heating in my partner's house (currently rented out).

Description of the problem is slightly vague, but apparently after the hot water has been on, the central heating has to be turned on manually at the programmer. Originally I assumed a programmer fault, but was subsequently told it could only be turned on after waiting some time. A gas fitter replacing a valve on the boiler suggested a problem with the motorised valve. (The tenants have lived with the problem since moving in 18 months ago before telling us, and the previous tenant was hardly ever there, so the problem may have been there for some time.)

System is an ancient boiler originally with gravity DHW, modernised 7 - 8 years ago - Danfoss FP715 Programmer, room thermostat, cylinder thermostat, 3 port motorised valve. (I think everything was Danfoss.) My partner lived in the house for several years after the upgrade and it worked fine, so it's not an installation problem.

I assume this has to be the valve or the programmer - what do I do to diagnose which? Any help appreciated.

 

[petertheplumber12]

The 3 port valve fails in hot water position by default so heating won't work because motor in the 3 port valve head needs replacing. or the head can be replaced. if it is Honeywell then just motor can be replaced. If not then whole head can be replaced usually.