Boiler boiling ?

[point5clue]

Hi All,
I have an Ideal Classic FF280. Mostly it is very reliable, but from time to time there has been a terrible rumbling in the boiler/airing cupboard until the boiler trips out. Once reset on the little switch on the side its back to normal.

It hasn't happed very often but I've established that it only happens when the hot water is on, but the radiators are not.

When I turned the boiler thermostat down to about two and a half it stopped happening. I'd almost forgotten about it.

However recently with the colder weather I noticed that the tank takes longer to heat up especially on cold days when the heating is on for longer.

So yesterday I turned the dial up to 3 and just now its gone again.

Given it seems to be a threshold thing, is there a component that can be replaced that might be the problem (or eliminate it from the mix) ? Or even adjusted ?

I'm very happy to have a competent engineer do the work, but given its so intermittent I'd like to diagnose it as far as possible in my own time before calling someone in.

 

[ianmcd]

It is common for the thermistor on these to play up and cause the fault you describe, they are not the usual thermistors but a long piece of cable with a sensor built into the cable, better if you get someone experienced to change it, can be other causes as well of course

 

[point5clue]

Thanks Ian,
After a bit of research I've educated myself on thermistors, and checked this one - its showing infinite resistance, so I think its worth replacing it.

I'm going to swap it and see if the situation improves.

 

[ianmcd]

I will get dogs abuse on here because it means working within the combustion chamber but make sure the boiler is nice and hot when you remove the existing one or it wont come out , when the heat exchanger is hot it is a lot easier to remove the probe