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One for the boiler experts/heating engineers
russbost - 11/12/12 at 10:27 AM

I have a Worcester Bosch 30CDI Greenstar condensing boiler, ordinary heating system with header tank it's not a combi or pressurised etc.

Boiler is about 2 years old & working perfectly, but sometimes, particularly on it's first fire up of the day (about 6am so this is kind of annoying as it wakes us up!) it makes a humming/buzzing noise, possibly a better description might be droning as when you're half asleep you imagine it's an aircraft overhead, but then it doesn't go away!

If you turn the system off at the time clock, wait 10 seconds then turn back on it is then quiet, usually for the rest of the day, occasionaly it will make some noise when it fires up later in the day (always seems to be when it refires rather than if it is already running I think, but can't be certain) but this is much quieter than the one it does in the night & again if turned off then back on it is then quiet.

I've done the usual Googling, but haven't found anything definite, it can't be an issue with the condensate pipe freezing as this vents into a 2" drain within the property before going outside.

It sounds a bit like a dry bearing or play in a bearing on a fan or pump, something of that nature, but as I can't get it to do it to order, I really don't want to be paying a plumber for half a day standing watching it!

It's not throwing up any error codes - any ideas welcome!

cliftyhanger - 11/12/12 at 11:07 AM

Not the motor in the 3 port valve? One I have in a rental is a bit noisy, seems to take a while to changeover too.

russbost - 11/12/12 at 11:50 AM

Don't think it can be the 3 port valve, that's in the airing cupboard & the boiler is 20 feet away from there (& one storey removed!)

big-vee-twin - 11/12/12 at 12:35 PM

It may be the fan located in the flue

MakeEverything - 11/12/12 at 02:08 PM

quote:
Originally posted by big-vee-twin
It may be the fan located in the flue


+1 for flue fan. could be sticking. does it lock out (stop working) after 30 seconds if you leave it or will it fire up whislt humming? the flue fan will have a flow failure switch on it.

Wadders - 11/12/12 at 03:34 PM

The Greenstar is blown gas and air, it's highly unlikely to be the fan.
Pump possibly, but difficult to know without being stood in front of it.

Al


+1 for flue fan. could be sticking. does it lock out (stop working) after 30 seconds if you leave it or will it fire up whislt humming? the flue fan will have a flow failure switch on it.

clanger - 11/12/12 at 06:10 PM

google "kettling"
might be a flow problem, try turning the boiler stat down a smidge and see if it helps ???

[Edited on 11/12/12 by clanger]

Andy S - 11/12/12 at 06:20 PM

It can also be flame flutter on the pre-mix burner head - Pre-mix are a little sensitive at times and can build a harmonic on the burner head - this can be at all sorts for frequencies ranging form low humming to high pitch howls and can happen at low fire rate or high fire rate. It can also change depending on atmospheric conditions like inlet air temps and pressures.

Then again it may just be the balance of the fan - yes it can be the fan if it throws a balance weight - If its on start up then its at max rate when the fan will be going flat out and so will the burner head - the burner head may stop humming when it has some temperature in it and the fan may stop after a while as the boiler modulates down from high fire.

you give it could be neither.As one mans blue is another mans green your description could be of something completely different.

russbost - 11/12/12 at 07:02 PM

quote:
Originally posted by MakeEverything
quote:
Originally posted by big-vee-twin
It may be the fan located in the flue


+1 for flue fan. could be sticking. does it lock out (stop working) after 30 seconds if you leave it or will it fire up whislt humming? the flue fan will have a flow failure switch on it.


It works perfectly, no lockout, no codes or anything just that it's noisy (sometimes) on first fire up after it's been off for a while, it did it during the day today, but much quieter & just went away after a couple of minutes without me doing anything.

russbost - 11/12/12 at 07:03 PM

quote:
Originally posted by clanger
google "kettling"
might be a flow problem, try turning the boiler stat down a smidge and see if it helps ???

[Edited on 11/12/12 by clanger]


Nothing like as noisy or harsh as kettling, had that with the previous boiler, a Potterton, I thought it was going to explode it was so noisy!

russbost - 11/12/12 at 07:06 PM

quote:
Originally posted by Andy S
It can also be flame flutter on the pre-mix burner head - Pre-mix are a little sensitive at times and can build a harmonic on the burner head - this can be at all sorts for frequencies ranging form low humming to high pitch howls and can happen at low fire rate or high fire rate. It can also change depending on atmospheric conditions like inlet air temps and pressures.

Then again it may just be the balance of the fan - yes it can be the fan if it throws a balance weight - If its on start up then its at max rate when the fan will be going flat out and so will the burner head - the burner head may stop humming when it has some temperature in it and the fan may stop after a while as the boiler modulates down from high fire.

you give it could be neither.As one mans blue is another mans green your description could be of something completely different.


This sounds a lot more likely as if left it does go away on its own, tho' seems to take a while sometimes, the burner pr mix sounds most likely, I have been told to try cleaning the condensate trap out first so will give that a try tomo.

As usual thanx for the help guys!