Banging when HW zone valve shuts

[Dev1872]

Alright lads looking for some advice. Had a situation where every time the hot water zone valve shut there was a loud bang. The customer said this also happened last thing at night when heating goes off too but didn't happen with central heating valve when I was there. It's an open vented system, S plan but no room stat. Boiler is a Potterton Suprima 50HE. I noticed a manual by pass (gate valve,) if this was opened about half way the noise did subside but not ideal to have it open that much!! Puzzling me as system design isn't my strong point, any help appreciated.

 

[gasmanrob]

Bet it's even quieter with the pump speed turned down. Valves close to the pump say 30cm?

 

[townfanjon]

auto bypass ???

 

[Dev1872]

Tried turning the pump speed down, same problem. I'm going back with an auto bypass I was thinking this would solve it? Valves are a about 6m from pump.

 

[gasmanrob]

6meters rules out pump slam. Worn valve did you try taking the head off and moving the lever by hand see if the flow takes over?

 

[Dev1872]

Yeah tried moving by hand, valve head and body are less than 18 months old.

 

[gasmanrob]

I only say because I has one do it straight out the box. Blooming thing

 

[Chalked]

Motorised valve fitted the wrong way ?

 

[gasmanrob]

State the obvious but valves and pump are pointing the right way?

 

[gasmanrob]

Motorised valve fitted the wrong way ?

Beat me to it

 

[Dev1872]

Yeah that was the first thing I checked, knew if it was wrong way it could cause a bang.

 

[Dev1872]

To be fair only checked if valves were right way, maybe naively thought surely pump couldn't be wrong!