"JohnW" wrote

snip...

You may want to check the setting of the auto bypass valve. I had a
boiler replaced last year, and it looked like the installer forgot to
set up the bypass valve. This caused some banging when the stats
switched. I adjusted the bypass and it cleared the problem.

John

Seconded.

Although the poor setting of mine didn't initially cause banging - that came
later.
Because the by-pass valve never opened, the boiler went into alarm state
when all the zone valves closed.
Also the pump over-ran for ages to try to dissipate the boiler heat.

Banging started much later and was resolved (for now at least) by turning
off the system, winding the by-pass valve fully closed - then fully open -
then back to its correct setting.

Maybe it would be better to sling these things and just use the old
fashioned 15mm balance line to ensure some flow is maintained across the
boiler?

Phil