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Mike Smith[_3_] Mike Smith[_3_] is offline
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Default Water hammer in central heating system pipes


"TheScullster" wrote in message
...

"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


Thanks for the idea's guys. The bypass valve (honeywell du144) is
set to the widest open position. At least I think so. The brass knurled
nut is fully anti-clockwise. FWIW I am also getting very long pump
over-run times. The boiler is set to 75c.

Can we rule out a faulty zone valve as the cause? My theory is that
the wet part of the valve is sometimes sticking when the motor is
deactivated,
but then the return spring wins the battle and closes the valve with a short
sharp shock. Most of the advice I came across in the web for
water hammer was to sort out the pipework but in this case the
pipework has been working for the last 10 years (or so) and the
water hammer only showed up ~6 months ago.

Thanks again....