banging air?

[sym]

When our heating switches off we get a very loud banging noise from our system. It only happens on the heating. The pump is installed so that it pumps down, is it possible that air produced by cavitation by the pump is released when it stops and causes the noise.

 

[oldplumber]

boiler kettling possibly if ch pump doesnt have an overrun facilty and hot water is on a gravity primary to coil in cyl so can continue to circulate if boiler goes off.

 

[sym]

It's a fully pumped system, with pump overrun.

 

[aggis]

Could do with checking that the pump runs on after clock turns off. If not check there is a permanent live feed into boiler. If ok or maybe even still change the boiler/overrun stat, as it maybe out of calibration.
Is the boiler noisy when running [ kettling sound ] , also check rads when heating if cold spot at bottom middle, system needs flushing, pref power & chemicals.
If boiler just kettling, can add sentiel x200 or fernox F2 noise reducer [won't cure, just like taking cough medicine, it'll be better for a while!]
Another thought, if it's just 1 loud bang on shutting down check your motorized valves.