boiler not switching off

[Rakker]

Hi. I have an Ideal Classic FF280 which works fine most of the time, but recently it has failed to go off on two occasions when the thermostat has switched off. Both times I switched the boiler off manually at the rocker switch and then switched it on again, and the boiler then seems to be fine again. Any ideas? I am not a plumber but a fairly competent diy'er.

 

[ianmcd]

More than likely an external control fault, you should have either 2 x 2 port motorised valves (S Plan) or 1 x 3 way motorised valve (Y plan ) the fault is most likely with these depending what system you have

 

[Rakker]

Thanks for the reply ianmcd. Could you explain the principle how these motorised valves control the boiler? I assumed the roomstat controlled a relay in the boiler and that relay was somehow sticking, perhaps a loose connection.
The problem (boiler continued heating after roomstat had switched off call for heating) reoccurred once this evening, and this time I decided to leave it running instead of switching it off manually. It took about two minutes, but then the boiler did switch off and functioned perfectly for the rest of the evening (no further running on, but switching off within about 2 seconds of the roomstat clicking off).
I know of one motorised valve serving the hot water tank (it's a sealed system), but I can't see how this valve could be involved in this problem as the boiler hasn't actually been heating the water when it has run on.
Where might I find the motorised valves you're suggesting might be faulty (I'm afraid I don't know whether I have a Y or S system)

 

[Agile]

The motor valves have a contact which makes them act like a relay!

We have no idea of the layout of your property or even your address! Its unlikely that we can tell you where your valves are.

As you cannot even recognised these valves I would suggest you call a competent boiler engineer to visit you who will know what they look like and can do a spot the valve hunt!

Tony

 

[Rakker]

Thanks for nothing, Tony. If didn't know what a motorised valve looked like, a quick google images search for "motorised valve" would yield almost as many thankless (probably because they're useless) posts as you've made on this site.
As for needing to know my address, I doubt that would help you as I'm fairly convinced the problem lies with a motorised valve at my neighbour's place.

 

[ianmcd]

The way that the motorised valves work is that they are powered by an independent motor for each valve and when this motor is actuated it closes a micro switch which sends power to the boiler and pump, a Y plan is different but works on a similar principle, it sounds like either one of these motors is sticking or the micro switch (end switch) is sticking

 

[Rakker]

Thanks again ianmcd. I did not know that the boiler is actually controlled by the motorised valves, but it makes sense.
I've got an S plan, with two 2-port valves. The CH has a Lifestyle valve (as opposed to a Honeywell valve regulating the HW), but it's working fine at the moment (lever returning to closed position as soon as call for heat stops and boiler switching off immediately). Can one tell which bit is sticking by watching the lever when the boiler does run-on? I'm guessing that a delay in the lever returning after stat switches off implicates the motor or valve, whereas a delay in the boiler switching off after the lever returns implicates the microswitch (this seems potentially catastrophic if the pump stays on while the valves are shut...?).
I've seen other posts suggesting that a sticking valve can be resurrected with a bit of cleaning and lubing, so I'm hoping to give that a shot.

 

[Rakker]

Sticking valve confirmed - lever stayed in "on" position after call for heat had gone off, but then, a minute or so later, returned to the "off" position with a bit of whirring. Many thanks ianmcd with the correct diagnosis and help with understanding. Will update on how I get on with the repair - hopefully just clean and lube, or second best replace motor; don't really want to have to drain the whole system to replace the whole valve, especially in it's awkward position stuck down the side of the HW tank.