Water hammer in heating system

[AllyBongo]

Fitted a Potterton Promax 24SL a few weeks ago, new zone valves and RF2 pack. Boiler is fitted to an open vent system and is fitted exactly to the MI's, close coupled F&E, vent pipe at correct height and angle. However, when the heating ZV closes, there is slight water hammer, and the vent pipe can be heard expanding. At first the vent wasnt as per MI's and a short blast of water came over it. After i re-piped it, this stopped. The MI's dont require a bypass, so one is not fitted, as some of the rads dont have TRV's and there is no over run. Though about fitting one, but i tried holding the HW valve open when the CH one shut and the noise was still present. Any ideas? OR anyone came across this before?

 

[Aquazone]

Only had this once, and it was the zone valve fitted wrong way round. Was a Drayton valve, and the paddle shut against the valve seat In same direction as pump and paddle chattered against seat.

Turned the valve around so paddle drops onto seat all sorted.

 

[Millsy 82]

Yeah heating valve wrong way round, I would put an automatic bypass on it though as I'm guessing it is an s plan.

 

[AllyBongo]

Cheers for the reply, its the correct way round though.

Planning trying a different zone valve on it this Friday.

 

[AllyBongo]

Yeah heating valve wrong way round, I would put an automatic bypass on it though as I'm guessing it is an s plan.

Yes its an S plan. Why would you fit a bypass?

 

[Millsy 82]

Because when both valves shut off the pump will be pumping against nothing. Even if it is only for a few seconds.

 

[AllyBongo]

Wouldn't of thought so, the micro switch will switch off the boiler and pump before the spring closes the valve.

Potterton were out for a look this morning and didn't mention anything about a bypass. As the MI's state, the boiler does not require one

 

[Millsy 82]

Wouldn't of thought so, the micro switch will switch off the boiler and pump before the spring closes the valve.

Potterton were out for a look this morning and didn't mention anything about a bypass. As the MI's state, the boiler does not require one

I was just always taught s plan fit an auto bypass for the reason above stops any noises occurring at a later date.

 

[AllyBongo]

Another new zone valve solved the problem! Two new Honeywell valves, only one closed one second slower than the other