The CH runs indepdant of the room stat when the HW is on.

[iantanton]

The CH continues to heat the rads even when the room stat is no longer calling for heat. However if the HW is turned off on the programmer then the room stat functions correctly. Can anybody help?

 

[twgas]

what type of system?

 

[hi-spec plumbing heating]

sounds like a sticky motorised valve if it's a system boiler set up

 

[iantanton]

It is a fully pumped system open vented system with a 3port valve which I think is a honeywell mid position type.

 

[hi-spec plumbing heating]

it's sounds like it's not shutting fully when heating not called for.
if from cold your hw is calling for heat does the rad side of valve heat up ?

 

[iantanton]

When the power is off the valve appears to be in the HW only position. The manual operation lever appears to run all the way to the left.

 

[hi-spec plumbing heating]

if from cold your hw is calling for heat does the rad side of valve heat up ?

 

[MANDATE]

You say when power is off valve appears to be HW only position.
It depends what you mean when you say 'power is off'. If you have removed the fuse, the spring should return motor and valve to HW only position.
But if you mean both HW and CH are switched off, then thats not quite the same, because there is still power on the grey wire of the valve.
It now depends which was the last side to be switched off. If valve was last at HW when it was switched off then valve stays at HW only position.
If valve was last at CH when it was switched off then valve stays at CH only position. All that has been cut off is the supply to fire the boiler.
It's been suggested valve may be sticking and letting water by and the proof is trying HW only to see if ch side is getting hot.
The outcome of this test is awaited.

 

[iantanton]

From cold I turned on HW only and there was no leaked into the CH circuit. The onlt thing that I did find was that the HW thermostate was set at 90. So I guess the boiler stat was controlling the HW temp. So I turned the HW stat to about 60. Everything now seems to be working ok. So I'm not sure if the valve had stuck but it certainly seems to be working ok now.
many thanks
Ian