boiler will not switch off!

[Monnie]

My Potterton Suprima 60 has decided to run the central heating continuously even with the thermostat and programmer off.
Any advice would be appreciated. Thanks

 

[Agile]

Without knowing how your system is configured its a bit difficult to make suggestions.

But it often turns out to be a motor valve fault.

Tony

 

[plumbingservices]

Boiler must be getting a demand somewhere roomstat or programmer fault possibly if you have external controls. Plumber/ gas fitter only, not a breakdown engineer.

 

[Monnie]

Thank you both for your advice. I'll get someone in to check it out.
Monnie

 

[MeldrewsMate]

Check that the heating valve isn't stuck open, or if a 3-port valve that it's not stuck at heating only position.

 

[Monnie]

Thanks for that.
Can you tell me how to check the valve. They are Honeywell valves. I don't know which type they are, but they have F6-9620 printed on the label. The system was installed in 1997.
The slider on top of the heating valve moves across very easily, while the slider on the hot water tank valve only shifts halfway.
Does that indicate a fault?