We have had a new Worcestershire Bosch 30i boiler. We have found during the day when room stat is set to 18 deg no problem, at night when we increase room stat to 22 deg there is an occasional humming noise and it stops when we turn the hot tap on.

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Kjh wrote in
roupdirect.com:

We have had a new Worcestershire Bosch 30i boiler. We have found
during the day when room stat is set to 18 deg no problem, at night
when we increase room stat to 22 deg there is an occasional humming
noise and it stops when we turn the hot tap on.


Flow resonance - try adjusting some lockshield valves to shange the flow.
Read up on "Balancing a Central Heating System" Could be a thermostative
valve being nearly closed and vibrating in the flow.

On 15/01/2021 00:03, JohnP wrote:
Kjh wrote in
roupdirect.com:

We have had a new Worcestershire Bosch 30i boiler. We have found
during the day when room stat is set to 18 deg no problem, at night
when we increase room stat to 22 deg there is an occasional humming
noise and it stops when we turn the hot tap on.


Flow resonance - try adjusting some lockshield valves to shange the flow.
Read up on "Balancing a Central Heating System" Could be a thermostative
valve being nearly closed and vibrating in the flow.


I had something similar and cured by slightly reducing the gas flow to
the gas burner.

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It very much depends on where its actually coming from, both ideas here
could be the case, and my neighbour had a pump that occasionally shifted and
made contact with a wall, transmitting the motor buzz all around the house
and also here next door.
Brian

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"alan_m" wrote in message
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On 15/01/2021 00:03, JohnP wrote:
Kjh wrote in
roupdirect.com:

We have had a new Worcestershire Bosch 30i boiler. We have found
during the day when room stat is set to 18 deg no problem, at night
when we increase room stat to 22 deg there is an occasional humming
noise and it stops when we turn the hot tap on.


Flow resonance - try adjusting some lockshield valves to shange the flow.
Read up on "Balancing a Central Heating System" Could be a thermostative
valve being nearly closed and vibrating in the flow.


I had something similar and cured by slightly reducing the gas flow to the
gas burner.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Fri, 15 Jan 2021 08:25:56 -0000, "Brian Gaff \(Sofa\)"
wrote:

It very much depends on where its actually coming from, both ideas here
could be the case, and my neighbour had a pump that occasionally shifted and
made contact with a wall, transmitting the motor buzz all around the house
and also here next door.
Brian
I had similar symptoms with the pump, got annoyingly loud after a few
years. Had a new pump fitted, totally quiet again, and rads getting
warmer, faster. Dismantled the old (10 year old Grunfos) pump, just
separated the motor from the cast body, and found that the impeller
was almost totally clogged up with hardened "sludge". The design of
the impeller has narrow passages between its input and output edges,
which can get easily clogged. I could have got away with just cleaning
it if I'd known about this.
Have now had the system power flushed and a Magnaclean filter fitted.

On 15/01/2021 11:10, Davidm wrote:
On Fri, 15 Jan 2021 08:25:56 -0000, "Brian Gaff \(Sofa\)"
wrote:

It very much depends on where its actually coming from, both ideas here
could be the case, and my neighbour had a pump that occasionally shifted and
made contact with a wall, transmitting the motor buzz all around the house
and also here next door.
Brian
I had similar symptoms with the pump, got annoyingly loud after a few
years. Had a new pump fitted, totally quiet again, and rads getting
warmer, faster. Dismantled the old (10 year old Grunfos) pump, just
separated the motor from the cast body, and found that the impeller
was almost totally clogged up with hardened "sludge". The design of
the impeller has narrow passages between its input and output edges,
which can get easily clogged. I could have got away with just cleaning
it if I'd known about this.
Have now had the system power flushed and a Magnaclean filter fitted.


In my case I had the problem when the circulating water reached it final
temperature. Switching from CH to CH + water would stop the problem for
a short while until again the water in the system reached the final
stable temperature. Manually turning off individual radiators etc.
didn't make any difference nor did the automatic shutting down of the
thermostatic radiator valves. Increasing the pump speed could reduce the
problem (volume of noise) but this caused over-pumping into the
expansion tank.

So, firing the boiler from a cold system resulted in no
buzzing/vibration noise until water in the total system got to its final
stable temperature. The room thermostat was still calling for heat. The
buzzing/vibration started at a very low level and got progressively
worse over a period of 2 minutes. The boiler would now turn off for a 2
to 5 minutes. When switching back on it would be silent at first but as
the heat exchanger/water got hotter the buzzing/vibration would start
again getting louder until the boiler again cut off.

Although difficult to exactly pin-point the source I believe it was the
boiler itself and the buzzing/vibration was transmitted via the
connecting pipes.

As I previous wrote, turning down the gas to the burners totally cured
the problem and resulted in longer on times in the burner cycle.

I should also mention that this is a 20+ year old boiler/system[1] and
the problem only occurred the first winter after having a run of around
3 metres of gas pipe (in the path to the boiler) changed from 15mm to
22mm so the input pressure to the boiler may have marginally increased.

[1] At the time it was advertised/classed as a high efficiency boiler
with a copper heat exchanger rather than the older cast iron. The manual
claims an efficiency of around 90% !

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