Boiler won't turn off!

fwor

I have a very ordinary conventional hot water/central heating boiler (Ideal Classic FF270) with cylinder upstairs and a pumped primary (I think that's what it's called) and two electrically controlled valves.

The problem I have is that when the timer/controller says that the hot water should turn off, the pump doesn't - it just keeps running.

As far as I can tell, the problem doesn't seem to be the cylinder thermostat, as the water temperature is normal, and the boiler itself cycles on and off as you would expect to keep the water up to temperature. I'm also fairly sure that the timer is not the problem - I think that when it says its output is off, it actually is off.

Can anyone please advise whether these symptoms have an obvious explanation?

I should add that if I turn the whole system off at the mains and leave it for a few hours, when I turn back on again it will often have fixed itself and the pump will no longer be running - until the next timer on period, when it starts to misbehave again.

molerat

Hot water zone valve stuck open / sticky. The power through the valve micro switch is independent of the timer so if the valve is stuck open then it will fire up the boiler.

bridgedino

Is the boiler in your garage or loft?

Owain_Moneysaver

Another vote for sticky microswitch inside the motorised valve.

fwor

bridgedino wrote: »

Is the boiler in your garage or loft?

Nope - inside the house.

Thanks for the suggestions - I shall take a closer look at the HW zone valve.

Seronera

Could be pump overrun as all well.

Sterlingtimes

Same Ideal boiler; same problem that I had.


In my case, it was the motorised valves in the airing cupboard. NPower (under maintenance contract) tried a bodge fix by changing the motors without changing the valves. I had a plumber in to do the job properly and at the same time insert some isolator valves to ease a future fix. Boiler itself has not failed once in 18 years.

fwor

Seronera wrote: »

Could be pump overrun as all well.

No idea what pump overrun is, but I'll bear that in mind in case it's not the valves...

Sterlingtimes wrote: »

NPower (under maintenance contract) tried a bodge fix by changing the motors without changing the valves.

Just checked and the valves were a bit stiff - easier to turn now having had some oil put on the shaft, so it's working Ok at the moment. But I think the problem is the switch contact occasionally sticking open/closed, and the switch is not (easily) replaceable. However... with a bit of switch cleaner hopefully it will last out until the whole system gets replaced in the summer.

Thanks for the advice!