In an earlier contribution to this discussion,
Andy Hall wrote:


You may be able to alleviate this by changing the pump to a Grundfos
Alpha.

These automatically back off their power as the flow resistance
increases, which I suspect here is the reason for the noise.

Is there any danger of them backing off so much that there's insufficient
flow to cool the boiler during pump over-run conditions?
--
Cheers,
Set Square
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