On Friday, 6 January 2017 21:46:04 UTC, wrote:
On Friday, 6 January 2017 21:00:27 UTC, John Rumm wrote:

So this is a hammer in the CH primary system, not in the DHW take off
from the cylinder?

Has it always done this, or is it new?

What is the set point temp on the cylinder stat?

What kind of circulator pump is it? (and what speed is it set to?)


--
Cheers,

John.

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Thanks for your interest, John.

1) I *think* it's in the CH primary - hence me planning to try depressuring the hot water side and let it go through a heat up cycle to be certain.

I would say for definite that the cylinder HW outlet is not affected by vibration. Trouble is the noise is of a pitch, and reflected around in an airing cupboard, that makes it hard to localise - except by touch.

By touch I can say CH inlet and outlet to the cylinder affected equally, cold feed affected sometimes.

2) The noise issue has (I'm told) re-occurred from time-to-time over the 12 years (approx) of usage. Allegedly no problems in the early years, but has come and gone spontaneously after that.


The best way to pinpoint a noise is with a listening stick.
This can be a big screwdriver. You put the blade on the suspected source and press the handle against your ear (or rather the area just in front of your ear, not the actual ear hole.)

Try throttling one of the pump isolation valve (the down stream one).

Try opening and closing radiator valves.

You can get "flutter" on the obturating device on any valve due to wear. Zone valves are specially suspect.
I think this last may be your problem as you say the noise depends on shutting heating on/off. This is usually done by means of an "electric/zone valve".

Using listening stick, check the pressure relief valve inside the boiler.
(This maintains constant pressure in the system by opening as the radiator valves close.)

It is on a pipe linking flow and return pipes. (Adjusting this might help with the problem)