Combi Boiler - To Burn Or Not To Burn

[Tim]

My Ferroli Domina combi is 3 years old and has worked well except that the ignition gap has to be adjusted every Autumn.

This year the system is generating hot water and hot radiators. But something is wrong because in CH mode the boiler often fires up, runs for between a minute and 10 minutes, shuts down, waits for around 30 secs, fires up, ... The pump keeps running even when the burner shuts down. And in hot water mode the burner seems to shut down at random unless I keep the tap very open.

My thoughts were no use:

1. Maybe the ignition gap has closed. No real reason for this because the symptoms are that the boiler totally refuses to fire up, but it has happened every year.

1. Maybe a bird's nest in the flue ;-) I've seen boilers fire up and down if the flue isn't installed correctly and the waste gases get back into the inlet.

Any ideas where I should look next?

Thanks Tim

[Ed Sirett]

The boiler runs until the water in the radiators is warm (this can be quite a short while - 10 mins) for a combi boiler in a smallish flat. Afterwards the burner fires only when the water temperature falls.

The more recent and sophisticated models usually insert a delaying mechanism to prevent 'short cycling' as you describe.

If you are in any doubt as to whether the boiler is operating correctly or not you should get in some professional help.

A bird's nest would so block the flue that it wouldn't fire at all.

[Tim]

Thanks, Ed. This is a 6-bed house so the burner should keep on trucking for a while. The key symptom is probably losing hot water unless the tap is very open. I'll muse on this, then post a search for a recommended heating guy in Felixstowe, Suffolk.

Tim

[Ed Sirett]

I tend to make the assumption that combi boilers are not (arguably shouldn't be) usually fitted to 6 bed houses.

The symptom you describe is almost always due to some failure of the water flow detector. I'm not familiar with this model but very often this is a rubber diaphragm which has a small tear in it.

[Gav]

you could probably get away, as ed said, with a new rubber and seal kit for the diverter valve. although i have seen the microswitch on an ariston boiler bieng the problem. DO check the seal kit for damage before fitting as i have renewed them only to find it was split when purchased.

hth

[Tim]

Ed Siret wrote

Interesting. It worked just fine until it stopped working just fine ;-) And most of the bedrooms are for children who left home ages ago, so the heating is rarely running hard.

But what do you think is best for these three-floor+basement Victorian semis?

Thanks. I'll investigate withe Ferroli service and report back.

Tim

[Doctor Drivel]

You should never assume. The CH side may be more than adequate to cope. If the DHW is one bathroom then a good medium flow combi is fine. Then again two bathroom models are arounmd that can cope with DHW and CH too.