My parents Potterton Suprima...
They've having some building work done which required drain down
and rerouting of the boiler flow and return pipework. (Plumber
did open boiler casing looking for a drain cock for the boiler,
but it seems there isn't one and the plumber who installed it
10+ years ago didn't fit one.)

Anyway, boiler is now making a new noise. When I first heard it,
I assumed it was the builders running a cement mixer outside.
When they'd gone, I realised it was coming from the boiler.
Initially thought it must be fan out of balance and drumming on
the case. Took the casing off and started up the boiler (with
the gas supply off so it doesn't light), and the fan is fine.
Checked the little cooling blades on the other end of the shaft
are not making contact with the case, which they weren't.
Put it all back together, and the noise is gone when the boiler
fires up, but only for a minute, and as it runs the noise slowly
comes back. Actually, I realise that as this cycles on and off
(it's not a modulating burner), the noise builds up slowly
over that period towards being quite loud by the time the
burner cuts off. I already checked the pump, and there's no
vibration there or in the pipework near to it (it's some way
from the boiler, being in a different room).

My best guess at the moment is that it's a resonance which
is setting up in the flue. It does sound a bit like a giant
church organ pipe. I think it's far too uniform to be any
sort of kettling. There's enough power behind it that you
can feel the vibration on the upstairs floor above it.

However, I can't imagine what would have caused this to
start happening. Nothing has changed with the boiler or
flue positioning. It's possible the boiler might have
sucked in brick dust (giant angle grinders have been in
use rather near the flue terminal), but that was not
obviously visible under the burners, where there were
just a couple of dead wasps and spiders (I had serviced it
nearly a year ago). I have not looked down the flue pipe
to see if there's any obstruction, which I'll try and do
next time I'm there. Apart from the noise, the boiler is
actually working fine.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 20 Feb, 11:02, (Andrew Gabriel) wrote:
My parents Potterton Suprima...
They've having some building work done which required drain down
and rerouting of the boiler flow and return pipework. (Plumber
did open boiler casing looking for a drain cock for the boiler,
but it seems there isn't one and the plumber who installed it
10+ years ago didn't fit one.)

Anyway, boiler is now making a new noise. When I first heard it,
I assumed it was the builders running a cement mixer outside.
When they'd gone, I realised it was coming from the boiler.
Initially thought it must be fan out of balance and drumming on
the case. Took the casing off and started up the boiler (with
the gas supply off so it doesn't light), and the fan is fine.
Checked the little cooling blades on the other end of the shaft
are not making contact with the case, which they weren't.
Put it all back together, and the noise is gone when the boiler
fires up, but only for a minute, and as it runs the noise slowly
comes back. Actually, I realise that as this cycles on and off
(it's not a modulating burner), the noise builds up slowly
over that period towards being quite loud by the time the
burner cuts off. I already checked the pump, and there's no
vibration there or in the pipework near to it (it's some way
from the boiler, being in a different room).

My best guess at the moment is that it's a resonance which
is setting up in the flue. It does sound a bit like a giant
church organ pipe. I think it's far too uniform to be any
sort of kettling. There's enough power behind it that you
can feel the vibration on the upstairs floor above it.

However, I can't imagine what would have caused this to
start happening. Nothing has changed with the boiler or
flue positioning. It's possible the boiler might have
sucked in brick dust (giant angle grinders have been in
use rather near the flue terminal), but that was not
obviously visible under the burners, where there were
just a couple of dead wasps and spiders (I had serviced it
nearly a year ago). I have not looked down the flue pipe
to see if there's any obstruction, which I'll try and do
next time I'm there. Apart from the noise, the boiler is
actually working fine.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

I'd be looking for a problem with the wet stuff. Is the reflled system
dosed correctly?
You may care to try some "boiler noise silencer"

In article ,
cynic writes:

I'd be looking for a problem with the wet stuff. Is the reflled system
dosed correctly?
You may care to try some "boiler noise silencer"

I doubt it's dosed at all - it still has to be drained again
(next week I think) to connect two more radiators on. The noise is
far too uniform/regular to be kettling. I'll see if I can sense
the vibration on the boiler pipework next time I visit. As I
said, there was none detectable at the pump, but that's quite
distant from the boiler.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
John Rumm writes:
Andrew Gabriel wrote:
In article ,
cynic writes:
I'd be looking for a problem with the wet stuff. Is the reflled system
dosed correctly?
You may care to try some "boiler noise silencer"

I doubt it's dosed at all - it still has to be drained again
(next week I think) to connect two more radiators on. The noise is
far too uniform/regular to be kettling. I'll see if I can sense
the vibration on the boiler pipework next time I visit. As I
said, there was none detectable at the pump, but that's quite
distant from the boiler.

Makes you wonder if its something resulting from air dissolved in the
new water. Still that ought to improve in a few days if that were the case.

Found it - it is coming from the pump. I bled the back of the pump
rotor bearing, a little air came out, and it instantly stops
making the noise. However, after about 20 minutes, it's back again.
Somehow, the pump bearing is getting and trapping air in it. The
pump hasn't moved, still looks to be oriented correctly. Didn't
have time to investigate much further - probably wait until the
new part of the heating system is connected up. Interesting how
this happens as the water heats, but stops the instant the boiler
cycles off (even though pump continues running). Could be related
to dissolved air coming out when heated.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]