central heating problem.

[mfgs]

Not sure if this is the best place to post this, but normally get more detailed answers off the public forum. I went to look at a job earlier, complaint of banging and pressure gauge jumping. Basically its a sealed heating system, unvented cylinder etc. When the hot water valve closes down there is a loud repeated bang for a few seconds and then stops. With every bang the pressure gauge jumps about. The expansion vessel, prv and gauge are all on the hot water return. There are also two heating zones, one for rads and one for underfloor. No issues with noise related to these two. One thing I noticed is when the auto bypass is open as much as it can be it practically cures the problem, only a couple of little knocks on the gauge, and then with it more closed down the problem gets worse. I am thinking maybe the pump is knocking the two port on the heating open a little bit causing the bang? Just don't know if I am overlooking something??

 

[buckley plumb]

is the zone valve the correct way around seen them slam shut before

 

[mfgs]

Yeah its the right way round. Also forgot to add that there is no balancing valve on the hot water return either. I have a video of the noise on my phone but don't know how to post it?

 

[zeebeedee]

Could need a bypass installing, could be starting to cause problems as it gets sludged up

 

[mfgs]

It has an auto bypass fitted. Sludge could be an issue. Don't think its a bypass issue though as it only happens when the hot water zone valve closes and not with the other two zone valves.

 

[zeebeedee]

Had a similar situation 2 days ago. When the cylinder stat shut down the system banged and vibrated! Adjusted the manual bypass and all was good!

 

[mfgs]

If the bypass was an issue it would bang when all zone valves closed down, not just the hot water. The fact that it only happens when the hot water valve closes surely points more to an issue with that side of things. As the bypass will act the same if any zone valve is opened and closed.

 

[Deleted member 44451]

sounds like aproblem with the hw zone valve to me,

 

[kozak1968]

What size and how close is the pump in relation to the motorised valves.

 

[zeebeedee]

If the bypass was an issue it would bang when all zone valves closed down, not just the hot water. The fact that it only happens when the hot water valve closes surely points more to an issue with that side of things. As the bypass will act the same if any zone valve is opened and closed.

This was a bypass just on the hw

 

[mfgs]

What size and how close is the pump in relation to the motorised valves.

Its a keston system boiler so the pump is inbuilt, not sure what pump they have in them. The zone valves are about 800mm from the boiler at a rough guess.

 

[tom609]

i have had zone valves banging in the past changed the valve and cured the problem it was a honeywell 2 port

 

[kozak1968]

If the zone valves are worn they can bounce when the pump kicks in

 

[plumber0808]

Got to be the two port valve. If your unsure swap the bypass with a new one while changing the two port.

 

[buckley plumb]

i would swap the valve - some zone valves dont have a spring rtn ball in them they have a hollow spindle which would not slam shut. could need a bypass as flow through just the hw circuit would be more than the htg .