central heating always on

[dneill]

Trying to sort out problem in parents house. The radiators are always on when the system is on and will not respond to room themostat which I have tested and works. Boiler only stops firing if programmer is put to heating only rather than heating and hot water. It also goes off if tank thermostat is turned right down.

There is only one motorised valve.

Ideas gratefully received.

 

[seco services]

does it go off when the cylinder stat reaches temp ? rather than turned down.



what valve make/model is it ?

 

[dneill]

Valve is sunvic sd 2752 and the boiler only goes off if the tank thermostat is turned all the way down. I have noticed that there seems to be no "click" when turning the tank thermostat as there is on the room thermostat. Do they work differently?

 

[seco services]

sounds like the stat not shutting off.
and the motorised valve is passing.
if the hw on only the rads still are getting hot ?
is the hw from taps really hot ?

 

[matt1e]

sounds like the stat not shutting off.
and the motorised valve is passing.
if the hw on only the rads still are getting hot ?
is the hw from taps really hot ?

Just another question to add to secos post
has the system ever worked properly? as may be a wiring issue

 

[dneill]

Turned out to be tank thermostat. Replaced and everything fine.
Thanks very much for help.