S plan heating water hammer issue.

[MrPotts]

I have a gas boiler and s plan configuration. More often than not whenever the CH motorised valve closes i hear water hammer, just a single thud, its been happening for quite a while. This only happens with the CH motorised valve, the DHW motorised valve works as expected with no water hammer when it closes. I have a Honeywell auto bypass valve which is on the default setting of 2. Could it be an issue with the motorised valve?

Edited April 22 by MrPotts

[ProDave]

Check when the CH goes off that the pump stops (assuming no DHW demand also) and the boiler stops.

 

My guess would be the feedback switch in the CH valve has failed and the pump is still running because it has not opened and the thud is the water diverting to the bypass valve.

[MrPotts]

54 minutes ago, ProDave said:

Check when the CH goes off that the pump stops (assuming no DHW demand also) and the boiler stops.

 

My guess would be the feedback switch in the CH valve has failed and the pump is still running because it has not opened and the thud is the water diverting to the bypass valve.

I have a system boiler with the pump controlled by the boiler pcb with a 3 minute pump overrun. This is normal operation. My thoughts are that either the motorised valve or the ABV is the problem.

Edited April 22 by MrPotts