faulty diverter valve

[johnbuckley]

I have a problem that the heating to my radiators does not switch off despite the wall control unit indicating the CH is off, the heating also does not go off when I turn down the room thermostat.
The only way that I can get the heating off is to cut the power to the control unit by switching off the fused switch at the wall.
The boiler is a Potterton Suprima
There is a hot water cylinder upstairs. Tribune HE Indirect 150L
I have searched this site and it seems that it is probably a faulty diverter valve.
Looking in the cupboard which contains the hot water cylinder I can see two items which I am guessing are the valves.
One is connected to the pipe between the primary coil in the bottom of the HW cylinder and the pump, it has an adjustment from ‘Flat to Open’.

The other is labelled ‘Myson Power Extra’ It has an orange operating light and a sliding adjuster which allows adjustment from auto to manual. It is set at Auto. On the cover of this valve it says @manual override only.
There are also 2 expansion vessels which sit above the HW cylinder.

I don't fully understand how this system works and I'm hoping, despite my poor description, someone will be able to advise me as to which, if any, of these valves are likely to be the cause of my heating problem.

Is there a way to test the culprit?
Thanks in advance.

 

[Armo74]

The valve to the heating circuit is probably stuck open. You can test this by removing the actuator which reveals a spindle and you should be able to turn it with your fingers. Make sure you cut off the electricity supply first.

 

[johnbuckley]

The valve to the heating circuit is probably stuck open. You can test this by removing the actuator which reveals a spindle and you should be able to turn it with your fingers. Make sure you cut off the electricity supply first.

Thanks for your reply.
Which of the two valves that I describe do you think will be the one to the heating circuit?
The 2 port valve with the 'flat/open' lever can be pulled off the pipe revealing the actual mechanical valve in the water pipe. Everything turns with finger pressure.

I haven't looked at the Myson Power Extra one as this is a bit awkward to get to.

 

[Armo74]

From your discription the myson one is the one you need to be looking at.

 

[johnbuckley]

Thanks armo74 I'll do some more research to see if changing this is a diy job.