I have a myson orion system boiler ,when the heating has been on and turned off by switch or room stat. The boiler,the primary flow and return bang like hell as there is water hammer in the system ,does anybody know if the boiler has a pump over run stat. If so where could i get one. Or any possible causes for this.Also when the stat is turned up on the boiler its becomes more frequent

cheers

jens, March 2009

Have you got a bypass leg fitted to the system. This allows the boiler to release its water back into the return leg until the overrun timer has completed it's time cycle. This prevents the pump from running into a dead end (Valves shut)

Doug, January 2010

all rads are open and working fine

jens, April 2009

have you turned any rads down or off

b, March 2009