Boiler won't switch off

[Ellie]

My boiler won't switch off via the timer or the thermostat, it just keeps firing.

I have turned it right down to zero. Is there anything else I can do before I can get a plumber to come out?

[Lurch]

On Sun, 4 Mar 2007 00:03:20 -0000, "Ellie" mused:

If you mean to turn it off, turn the spur off that should befitted somewhere, or unplug it.

[Frank Erskine]

You don't say what sort of boiler it is. Could it be a combi with preheat, which does maintain a small quantity of hot water in a sort of inbuilt cylinder? If so, the boiler will fire up for a few seconds every few minutes, unless you turn the preheat to zero.

A plumber would be of no use, anyway, unless you have leaking pipes.

[Ellie]

No it's not a combi. A Potterton balanced flue.

No - the one we usually have is corgi registered.

[Roger Mills]

Tell us a bit more about the system. Are there any motorised valves? If so, how many and what type (2-port or 3-port)?

My hunch is that you have an S-Plan system (see S-Plan in

) which has two 2-port valves. The valves are opened in response to signals from the programmer and thermostats (room and cylinder). Auxillary contacts in the valve's actuators switch on the boiler and pump when either or both valves are open.

If one of these valves sticks open, it will continue to fire the boiler even if the programmer and stats are not calling for heat - which would appear to fit your symptoms exactly.

Whether or not you can do anything yourself depends on how competent to feel to remove the actuators from the valves and check that the spindles of the working parts of the valves are free to turn. If the spring return in an actuator moves it to the closed position as soon as you lift it off the valve, that's a pretty good indication that the valve itself is seized in the open position. Another possibility is that the auxillary contacts in the actuator could have become welded together so as to be ON regardless of the position of the valve itself.

If you're unable to DIY it, you really need someone who understands both the plumbing and electrics of CH control systems.

[Ellie]

Thanks for the comprehensive reply. My husband is probably capable of the above so I will pass this on to him.