Combi boiler not responding to radiators

[matthew.larkin]

Hi

I've got an intermittent fault with a 5 year old combi boiler. Every

3-4 months or so the heating will pack up for a couple of days and then sort itself out.

What happens is that combi seems to stop responding to the water system by not delivering hot water through the central heating. The hot water taps work fine, the boiler fires up just as normal. But as far as the central heating goes, the boiler fires up every 10 minutes or so (perhaps less frequently), gives about 20 seconds of clicking and whirring (as usual) and then switches off. The obvious effect is that the radiators therefore don't get hot!!

The problem is that each time this happens, we give it 24 hours or so, then despair (and freeze), call a plumber and by the time they turn up (or schedule to turn up) the heating sorts itself out.

Any DIY suggestions for what I could do to investigate? I know the boiler itself is out of bounds, but do you think draining the system / cleaning the water in the radiators might help? Perhaps its a blockage in the system somewhere which means that there aren't enough pressure changes in the system to prompt the combi into action? I don't know much about this stuff, so any pointers gratefully received, either to do myself or to get a plumber in to at least try something constructive!

Thanks!

Matt

[Tony Bryer]

You'll increase the chance of a helpful answer if you tell us the make and model

[matthew.larkin]

you tell us the

"fundamental", rather than boiler specific. In fact, it may be completely unrelated to the boiler itself (as it produces hot water fine).

My gut feeling is that it is something to do with the circulation system itself (by which I mean the water flowing around the pipes, radiators and radiator thermostats) rather than the boiler which is causing the problem; and therefore any useful suggestions around that side of things would be useful.

One thing I should note; the top radiator in the house (in the converted attic) does seem to get a lot of air in it, to the extent that when I vented it the other day I had to re-prime the system with more water before it would force all of the air out of the system. But we don't seem to have any water leaks, so I don't see how air would be getting into the system.

I'll post the boiler details later on today, but thanks for reading and responding Tony.

Matt

[Ed Sirett]

you tell us the

It's almost certainly the diverter valve inside the combi. Make,model and date of installation would be useful.

[matthew.larkin]

if you tell us the

Its a Potterton Combi 100 - installed approx 6 years ago I believe.

Cheers!

Matt

[Ed Sirett]

if you tell us the

I think that model has a conventional water flow diaphragm and diverter valve unit. I'm surprised that it is an intermittent fault though.

[matthew.larkin]

Its literally 4 times in the last 2 years (since we've been in the house) for a max of 2 days at a time (3 of those times have been on a Friday evening, conveniently (not) enough!!).

The water from the rad's is fairly grimy when I've vented them, so its certainly not the cleanest system in the world. I'm sure some TLC wouldn't go amiss. The radiators are a mix of old and new too.

Anyway, got a recommended plumber coming round next week. Shame it will all be working fine by then though!!

Matt

[Ed Sirett]

Could well be debris in the primary circuit.