Boiler won't go off once ignited (until overheat cutoff)

[Gondorian]

Once ignited, the boiler (Tricom ProTherm 40-50 CI, 4 years old) in my vented system will not go off, causing it to eventually trigger the overheat cutoff (and much noise from my pump and pipework due to the insanely hot water inside).

I understand that a properly functioning boiler will ignite for maybe 20 mins to heat up the water and then automatically switch off until the heat has dropped enough to warrant coming back on briefly (e.g. 5 mins) to maintain the heat. This intermittent igniting should continue while I have my heating switched on.

This clearly isn't happening in my system. I have managed to simulate it and gain correct operation, by manually toggling my heating on and off to maintain the right temperature, which suggests that there is nothing else at fault besides my boiler.

Is this a correct assumption? All my rads have TRVs, and I do have a bypass, so I guess when all the rads are hot enough they close and the hot water goes round the bypass, which the boiler should sense is too hot. Is there any way to tell if it is the thermostat or the PCB at fault?

(Apologies to anyone who wasted any time reading my other thread. As you can see, I have streamlined my problem somewhat now.)

 

[gasgeezer]

The boiler is basically a glow-worm ultimate it should have a pump o/run if this is not working it is usually the pcb it could be the stat out of calibration call glow-worm they do a fixed fee repair and are based in derbyshire

 

[Gondorian]

Thanks for the reply.

The overrun operates for about 3 minutes after I turn off the heating, but I'm not sure how that could be the problem. In normal operation, I would have the heating on for a number of hours and expect the boiler to ignite on demand to keep a steady temperature. I thought the overrun, by definition, only runs after I've turned off my heating.

I phoned Gloworm earlier today and they said it would be £195 regardless of what the problem was (they didn't even attempt to ask me), but they can't get out to me until March 7th. If it is the stat or PCB, do you think someone local could do it for less?

 

[gasgeezer]

I would be inclined to go for the stat you can check this with clip on pipe therm. and see what the temp. is doing it should cut out at about 82degs plus or minus 3degs the o/heat kicks in around 95degs any engineer s/be able to diagnose this for you

 

[Gondorian]

Do you reckon I should I buy one of these clip on pipe thermometers and test it out before I call someone in? Since I am not competent enough to actually fix it, I guess whoever I call can diagnose it and fix on the spot.

More info: The other current quirk of this boiler at the moment - which is no doubt related to the problem described above - is that it only comes on if I turn the knob on the front to 0. According to the instructions on the front panel, this should turn the boiler off - not ON! Until a couple of days ago, when all my heating suddenly went off, everything was working fine with the knob set to MAX. It was at this point I turned it to 0 and managed to get it on, but with the overheating problem.

 

[gasgeezer]

sounds like the knob has moved out of synch leave it to an experienced engineer the boiler should not work in the 0 position

 

[Gondorian]

I have someone coming round tomorrow afternoon to look at it. I said I suspected it was the thermostat, but if I'm really lucky, it might be the knob is out of sync and he can fix it without ordering anything!

Thanks for your help.

 

[Gondorian]

Plumber came yesterday and confirmed my boiler was just a rebranded GlowWorm Ultimate. He also said it was the thermostat at fault and he'd had another one go wrong in exactly the same way the week before! He just phoned his parts supplier and said "same again".

He came round today and installed the new thermostat and all was sorted.

Thanks for your help, gasgeezer

 

[gasgeezer]

your welcome glad to be of help thanx for the feedback