Vaillant Ecotec 937 - Noise When Hot Water At Full Load

[Johntheo5]

Disappointing.
If it is clean then, despite the noise the boiler should now be able to achieve its full output of 37kW which would/should also be a check on whether the PHEX is actually clean. Did you clean it yourself?
Suggest setting the DHW temp to max, open up all HW taps, showers etc, after say 5minutes, take a snapshot of the gas meter and exactly 3 minutes later, to the very second, take another, shut off the HW users. Should expect ~ 41(kWh) when you multiply the gas meter difference X 220.

Schematic, below of the DHW system, so if the PHEX is clean then possibly points to the storage cylinders but can't really see how they might cause a problem.

 

[dunder101]

Disappointing indeed, but I think this 14.5 year old boiler is probably telling me something

I observed the PHEX being removed, cleaned, flushed and put back in place. It didn't look particularly dirty and, in fact, a new one was installed maybe six years ago not too long after we moved into this house. The system water quality was terrible and several new components were installed by Vaillant as part of a fixed price repair. Since then, I have been keeping an eye on he water quality annually and changing every two years.

Anyway, I did suspect the storage tanks or something else like that. The noise is at its loudest when I listen at the back, which is where the various valves and the pipes up into the storage tanks are.

The only component which I *know* is faulty is the cold water inlet valve. This was replaced as part of the above those years back because it was letting by slightly on the connection to the filling loop and the new one also started letting by a couple of years back in the same way. I understand that this is very common on Vaillants and also inevitable, and I have since blanked the connector to the the filling loop on the double check valve and leave it disconnected unless a top up is required. It can't imagine this is causing this noise and, if it did, why now all of a sudden ....

 

[Johntheo5]

Its a pity you couldn't convert this easily to a straight through combi boiler by bypassing the storage cylinders, at least that should/might give noisless 37kW output, I have read that the charging pump can give a droning noise if failing on high flowrates but your test was done with the boiler switched off. I think the 938 (if still on the market) has this facility or something like it, maybe no cylinder preheating.

Will you install another storage combi when you do change?, from my basic calcs it looks like you should get ~ 6/8 minutes with a 50% increase in flowrate before the 30L stores run out but I suppose the main advantage might be that HW tap(s) can be opened briefly while having a shower without any temperature drop.
Was this your experience?.

 

[dunder101]

I totally agree on the point about converting this to a normal combi and not using the storage tanks - my view is that they just add complexity and things to go wrong. This boiler was here when we moved in and was about five years old then. It has not been reliable at all, and I wouldn't buy a Vaillant myself based solely on this experience, but I know others have different views and have had much better experiences.

I wouldn't get a storage combi - we really don't need it or the additional things to go wrong. We're end of terrace, four bedrooms but only three of us live here, with two bathrooms - one with a bath (and shower over) and one with just a shower. I'm looking at the Ideal Logic+ 2 35 and the Alpha E-Tec NX 33 at the moment - I might pop in a new post to see if others have experiences of either these.

I really appreciate the time you've spent on this - thank you.