Loud clunk when HW or CH valve closes

[apswan]

I have recently had my central heating/HW system upgraded.
I have a Baxi Megaflow system HE boiler 2 x 2 port drayton ZA5 valves, plus a Boiler Buddy on the return to catch any bits in the old pipe system. Boiler and valves are located in the loft.
HW cylinder were also replaced along with pipework to HW cylinder. All CH pipes are from old installation apart from new linkage pipes from boiler in loft to old pipes in Garage below.

Also to state the obvious, it is a system boiler so pump, bypass, PRV, vent and expansion vessel are within the boiler enclosure space.

All was well from installation in mid november 2006. In the last month I have noticed a loud noise from the loft when either the heating or water shuts off.
I have tested today and found that the noise occurs just as either valve is closing and this happens even if the alternate valve is still open.

The valves are both close to the boiler (approx 1/2 Metre) on each leg of the feed after it splits for HW/CH

I would deduce from this that the valve is closing quickly and causing the pipe noise, the question is why has this just started to happen and what can be done to resolve it.

I am a fairly proficient DIY plumber, but had a Corgi registered heating engineer fit and commission the system.

I have tried running the system at 1 bar and 2 bar to see if this made any difference, but have not seen any change, although currently pressure is just over 2 bar when running.

Any advice welcome.

 

[Softus]

Does the pump have a speed selection control? If so what speed is it currently on?

 

[apswan]

I am not sure. This is not something that I have looked at as the pump in within the Boiler enclosure.

I will check later today and report back.

thanks

 

[meldrew's_mate]

Your symptoms suggest valve(s) installed the wrong way around, though why it should start making noises now rather than from the start has still to be deduced.
ACL Drayton valves have a flap type valve plug, and the direction of flow is clearly marked on the body.

So how do you tell which way the flow is going? Turn only the how water generation on (DHW only). Wait for this pipework to get hot, then have an assistant turn on the CH; feel the CH pipework each side of the valve, the side which gets hot first is the upstream end, check this implied direction against the arrow.

Most system boilers pump on the return side of the boiler, so a mistake can be made by the unwary. Also a bypass may not be integral to the boiler, check this out, and if not fitted an external one will need to be installed.

 

[ChrisR]

Try fixing the pipes a bit more firmly - can be all it is.

 

[apswan]

Thanks for your replies.

All pipework is very secure.

Pump does not have speed control according to Baxi.

I believe valves were installed right way round as I am sure I checked this at installation, but a quick observation last night did not make it obvious which end was A and B. I will have to check again when I get more time later.

The boiler install guide clearly shows which is flow and return, and the valves are installed on the flow side, but I need to double check that they are the right way round.

Will report back later today.

 

[apswan]

Finally managed to check and confirm that valves were the wrong way round.

The Drayton valves markings were underneath the valve with A B notation at appropriate end, however this was not evident due to the way the valves were installed. The actuator has a manual lever which is misleading as its A-B markings are opposite to Valve markings.

Initial findings seem to suggest that the problem is now fixed, although I have heard occasional noises of a similar nature, but not had time to figure out what is causing them.

For now things have certainly improved. Thanks to all contributors.