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]

Are the arrows on both valve bodies pointing in the direction of flow?. Also the circulating pump head may have been set very high but you can only check this yourself if externally fitted.

 

[Xrecymech]

Are the arrows on both valve bodies pointing in the direction of flow?. Also the circulating pump head may have been set very high but you can only check this yourself if externally fitted.

Yeah, the valves have arrows pointing in exactly same direction as with the old boiler. Pump is in boiler I guess (ideal Logic C30) can select pump speed through boiler front panel and looks like it has 2 speeds - 70% and 100%, tried at 70 and made no difference

 

[John.g]

Yes, they might be pointing in the same direction as with the old boiler, still could be wrong (unlikely) and didn't bang with old boiler/circ pump, costs nothing to recheck. Also, with the new type circ pumps which don't work like the old fixed speed pumps it can be nearly impossible to set up a ABV properly but hard to see this causing valve problems apart from either two much by pass or none.
But maybe set up just a slight bypass with both valves open, then see if banging persists when valves close.

 

[Xrecymech]

Yes, they might be pointing in the same direction as with the old boiler, still could be wrong (unlikely) and didn't bang with old boiler/circ pump, costs nothing to recheck. Also, with the new type circ pumps which don't work like the old fixed speed pumps it can be nearly impossible to set up a ABV properly but hard to see this causing valve problems apart from either two much by pass or none.
But maybe set up just a slight bypass with both valves open, then see if banging persists when valves close.

As far as I can tell flow through power valves is top to bottom and bypass flow is from right and then down, not sure how to check to be totally honest. This is on the return side I think as rads are hot for while before these pipes get hot. If CH and HW has been off and is cold, manual operation of valves and they close silently however, when hot but pump overrun complete, manually operating the valves and they bang when closing

 

[John.g]

It would be unusual to have mot.valves on the return, also the ABV bypasses from the flow to the return so the arrow would indicate that this is the flow side, if its the return then the by pass is the wrong way round, you will have to establish for sure which is which, maybe a few more pictures.

 

[Xrecymech]

I’ve just checked the pipe work into the new boiler and compared to pipe work placement against the old boiler and the pipe on the left on old boiler is CH return (Vokera Unica HE) and on the new boiler it’s CH Flow and it’s the same pipe it hasn’t been re-routed, hopefully I’ve got that wrong, would the heating work if that had actually happened?

 

[exedon2]

If the motorised valves have flow in wrong direction thats the cause of banging .

 

[John.g]

Just to get this clear, You are saying that the flow from your new boiler is now flowing through the return pipework and back through the flow? If so then then it is flowing upwards through the flow manifolod and its no wonder the mot. valves are banging and the ABV is the "wrong way" round, the heating will work mostly OK but the installation is completely wrong if I am interepreting you properly, (you also said this manifold was heating up later, more "proof" of wrong way circulation. Just confirm your findings and get back the boiler installers pronto.

 

[Xrecymech]

If the motorised valves have flow in wrong direction thats the cause of banging .

Yeah, that would tie in with what I have been told, it’s all making sense now, I just need an independent plumber to come around and verify my thoughts on the plumbing into the boiler, thanks for the help folks.

 

[Xrecymech]

Just to get this clear, You are saying that the flow from your new boiler is now flowing through the return pipework and back through the flow? If so then then it is flowing upwards through the flow manifolod and its no wonder the mot. valves are banging and the ABV is the "wrong way" round, the heating will work mostly OK but the installation is completely wrong if I am interepreting you properly, (you also said this manifold was heating up later, more "proof" of wrong way circulation. Just confirm your findings and get back the boiler installers pronto.

No It look like the flow and returns are connected up to the boiler the wrong way round

 

[John.g]

Yes, quite obviously, causing reverse circulation, I would get the original installers back, it was up to them (IMO) to check the correct orientation of the pipework especially if they removed the old boiler, why do you need a independent plumber?.

 

[Xrecymech]

Yes, quite obviously, causing reverse circulation, I would get the original installers back, it was up to them (IMO) to check the correct orientation of the pipework especially if they removed the old boiler, why do you need a independent plumber?.

I’ve been on to them for a week now saying this isn’t right and they have refused to do anything however, I have emailed them with pictures comparing the old/new pipe work and installation diagrams for old and new boilers, and told them I think they have installed wrong way round, I expect them to send someone round now

 

[Xrecymech]

Yes, quite obviously, causing reverse circulation, I would get the original installers back, it was up to them (IMO) to check the correct orientation of the pipework especially if they removed the old boiler, why do you need a independent plumber?.

Old boiler was Vokera and CH return is on far left, whereas new boiler is CH flow, photo of pipe work shows pipe on far left hasn’t been re-routed, just extended up to meet new boiler position on wall. Looks like hot water is wrong way round as well

 

[John.g]

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.

 

[Xrecymech]

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.

Not exactly sure on old boiler to be honest, presumably, and going by the pipe config in the installation docs, it had a separate return and flow for both hot water and CH (could programme them independently)

 

[John.g]

You could follow the cylinder coil return back to the boiler and see if that is connected properly at least and maybe trace some more pipework as well but you definitely need the installers back in.
As a matter of interest, could you run the DHW & the CH together on the old boiler?.

 

[Xrecymech]

Yeah think so, but hot water would come from storage tank would it not?

 

[John.g]

What I mean is could you heat them together, ie have the CH on and the DHW heating on at the same time , CH & DHW zone vaves opened together. (not a combi boiler?))

 

[Xrecymech]

Sorry, not sure to be honest with old boiler, can with new one though

 

[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