Heating system water hammer

[Adam a]

Getting water hammer when motorised 2 port Honeywell turns hot water off to the cylinder. Valve works fine and its the right way. System been in for years and its just started happing. Boiler pump keeps running which is correct to dissipate the heat but as soon as the hive turns the hot water off i get water hammer. Should there be a ABV installed ? But it’s been working fine for years. (Its like once the hive gives the signal to shut the valve it should stay open for few minutes to let boiler pump finish but it shuts straight off)

 

[cross thread]

The valve by the thermostat is a bypass try adjusting it

 

[danfre]

You should have a bypass before the motorised valve, it could be that you have one on a radiator or towel rail and it has been closed off.
Or you may find a auto bypass that needs adjusting

 

[Adam a]

Cracked that hand valve. Found an abv by the boiler. Replaced it and seems okay. Got it set on .3 not sure what it should be on.

 

[Adam a]

Systems been in since well before i moved in but is this picture correct. The flow goes in mid way and comes out the bottom. If thats the case the motorised valve is the wrong way round but its always been like this