Problem with bang in CH and HW

[Xrecymech]

Evening,

I appreciate this has been asked many times and I have tried what has already been said on this forum but still can’t resolve the issue. So, had new boiler fitted and later that day, when the motorised valves for CH and HW closed, they both bang once on closing. I tried to get the company out who fitted the boiler however, they said it wasn’t their issue as they didn’t change anything other than fit the boiler. I have changed one of the 2 port motorised valves (CH) and power head and also changed the bypass valve as the adjusting mechanism wasn’t working, ch and hw both work fine but the banging still happens. Other plumbers won’t look at it (I understand why) and still discussing with company who fitted the boiler to come out to sort. System is a combi with unvented tank Any ideas as to what else can be done try and fix? Cheers all

 

[John.g]

OK then, I probably don't understand the 4 pipe reason so, very old installations had the CH side pumped and the DHW gravity circulated and I thought the reason for having separate pumped CH & DHW was for the reasons I stated above, but allowing two heating systems on together sounds strange as the boiler can only run at one flow temperature.

 

[ShaunCorbs]

Your new boiler is a 4 pipe?, was the old boiler a 4 pipe as well? others will soon inform you, but think they should be two separate circuits, one for the DHW and the other for the CH, the boiler I think can then heat the cylinder very rapidly with very high temperature water and the CH (especially with weather compensation) can run with very low temperature CH water. Would also think that the DHH takes priority and that you can't have both on together but you can get all this checked out, I can't see a common manifold working, but maybe you can have a common flow manifold with separate returns.

its a combi boiler

 

[John.g]

Evening,

I appreciate this has been asked many times and I have tried what has already been said on this forum but still can’t resolve the issue. So, had new boiler fitted and later that day, when the motorised valves for CH and HW closed, they both bang once on closing. I tried to get the company out who fitted the boiler however, they said it wasn’t their issue as they didn’t change anything other than fit the boiler. I have changed one of the 2 port motorised valves (CH) and power head and also changed the bypass valve as the adjusting mechanism wasn’t working, ch and hw both work fine but the banging still happens. Other plumbers won’t look at it (I understand why) and still discussing with company who fitted the boiler to come out to sort. System is a combi with unvented tank Any ideas as to what else can be done try and fix? Cheers all

Just looking at this post again, have you got or had a hot water cylinder? and have you only got one motorised valve that serves all your CH requirements?, your installed boiler is now a combi boiler?.

 

[Xrecymech]

So it’s a combi with 2 valves off the flow, one valve manages CH and other manage hot water to the storage tank. There is one tap that comes straight from the boiler which is heated separately to the hot water storage (I guess in a traditional combi setup) so basically and it looks like to answer your previous point, I can have hot water at same time as CH as the CH water is what appears to heat the water in tank. That said, they’ve been back today and swapped the CH flow and return pipes and all is back to how it should be, and the knocking has gone