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carl-106 · Joined: 01 Jun 2008 Posts: 3 Location: Gloucestershire

Hiya,

I have a Celtic ff combi boiler which is making a droning noise like a fog horn that increases in intensity ...

It started after moving in and goes like this..

Turn on hot water tap
Stage one flame ignites...ok
Stage two flame ignites...noise builds up over about 2 secs
Hot water thermostat activates as water gets to temperature
Back to stage one flame...noise dissipates abruptly
stage two....noise back again

Water pipe post heater is approx 70 oC constant once warmed up

No noise at stage one flame during central heating operation

The noise is coming from the top of the boiler, I have done the following so far...

stripped / cleaned out the pump and filter assy (alot of debris)
stripped / cleaned out the change over valve assy (again alot of debris)
Checked hot water heat exchanger (clean)
flushed out individual boiler water pipes (where possible)
Ran cleaner through the system for a few weeks (X400)
Flushed that through (some debris came out but no change)

So far its has seemed like a water flow issue through the main heat exchanger, but could it be a fan/flue problem? (vibration)
Do I need to use a better system cleaner?

Any advise would be welcome.. Smile

Cheers!
Carl

chaza · Joined: 17 Mar 2007 Posts: 69 Location: MILTON KEYNES

i would check out the flue fan assm, although the ingition stages are working, the fan assm sound like its on the way out

AlanE · Posted: Tue Jun 03, 2008 9:51 am Post subject:

Or could be faulty water control valve that is vibrating due to water flow.

Does varying amount tap is openrd change pitch of the sound?

You say it's a combi boiler and describe symptoms in hot water mode. What happens when central heating only is on?

carl-106 · Joined: 01 Jun 2008 Posts: 3 Location: Gloucestershire

Hiya,

Thanks for your help Smile

On Central heating the system works on stage one burner only.... everything works great, no noise and all rads are up to temp.

With the hot water tap on, the water flow makes no change to the noise.

The only thing that sets it off is the stage two burner....at first i assumed it was the water overheating in the exchange due to a blockage.

Im now wondering if the extra heat / pressure when stage two fires up is causing the fan assy to start vibrating...?

Cheers!
Carl

AlanE · Posted: Wed Jun 04, 2008 8:11 am Post subject:

Presumably you are refering to the Celtic FF boiler GC. No 47 980 01.

When was the boiler last serviced? It could well be the fan that has worn bearings when it goes to high speed and gets hot. However it could also be due to incorrecly adjusted gas pressure to the burner.

I would suggest that you get a qualified boiler engineer in to check as setting gas pressure needs certain equipment.

carl-106 · Joined: 01 Jun 2008 Posts: 3 Location: Gloucestershire

Hi Alan,

Yes its the GC No 47 980 01, i believe it was checked over before we moved in.... it all started a couple of months later...tis the way it goes..lol

Thanks for your help....ill update when I know what it is.

Cheers!
Carl