Vaillant Ecotec 937 - Noise When Hot Water At Full Load

[dunder101]

Our Vaillant Ecotec 937 has started to make a wheezing steam train style noise when the hot water is at full load.

Here's a video of the noise: https://drive.google.com/file/d/1bbh6F_rNUn5JFascntT3CaWu_LQUx8Aa/view?usp=drivesdk

The hot water flow fluctuates and I reckon it is lower than a few weeks ago.

There is no noise when other hot taps or showers are in use, nor when the heating is on.

I thought the problem could be scale related so I put in some Sentinel X200 but no change yet. The system water is already reasonably clear, but my next throw of the device would be to put some Sentinel X400 cleaner into the system and let that do it's job before draining and refilling
(on the basis that the plate heat exchanger could have a partial blockage).

The boiler is 14 years old and we've had multiple repairs done on it in the 7 years we've lived here (dip tube replaced, new plate heat exchanger, new diverter valve, new PCB to name a few). It has not been reliable and I have no intention of spending hundreds of pounds on another repair - I would just replace it with a new boiler. But before I do so I'd welcome any thoughts and suggestions in case it could be a quick / easy fix.

Thanks in advance.

 

[Johntheo5]

The series "9" is a storage combi boiler, not sure exactly how they work but if you have a very high DHW demand do/don't they run cold for ~ 10 minutes to replinish the store. You have a 937, 37kW to hot water, so at a present 13C mains temp, the HW temp should not fluctuate at a flowrate of 14LPM or less at a HW temp of 50C or 11LPM at 60C or less, if the flowrate is say 18/20LPM then the water should eventually run cold for 10 minutes or so?. Can't comment on the noise.

 

[dunder101]

Thank you very much for your reply. It has been a few weeks so I thought I'd update here in case it is useful for anyone else.

I decided to roll the dice and ran some Sentinel X400 through the system. After a couple of days of both heating and hot water use the wheezing noise issue resolved itself and the flow rate stabilised. I thought, for a a few days, that I had totally lucked out and went ahead with draining the system and refilling with fresh water and inhibitor. Unfortunately the boiler then developed a strange clicking / sizzling noise when at full hot water load instead - https://drive.google.com/file/d/1-1FnYMFJKBdBC_KxWU-NWwLuOjHL47Wl/view?usp=sharing. It now sounds like it is coming from the storage tanks at the back of the boiler - maybe below. We still have heating, we still have hot water (albeit at what feels like a lower flow than before, and with that noise at ful load) so it's okay for now - and with the boiler being 15 years old this year I intend to replace it in the summer unless a miracle happens or anyone here recognises the issue and can point to a quick / cheap fix!

Thanks again everyone.

 

[SprunkiRetake]

Thank you very much for your reply. It has been a few weeks so I thought I'd update here in case it is useful for anyone else.

I decided to roll the dice and ran some Sentinel X400 through the system. After a couple of days of both heating and hot water use the wheezing noise issue resolved itself and the flow rate stabilised. I thought, for a a few days, that I had totally lucked out and went ahead with draining the system and refilling with fresh water and inhibitor. Unfortunately the boiler then developed a strange clicking / sizzling noise when at full hot water load instead - https://drive.google.com/file/d/1-1FnYMFJKBdBC_KxWU-NWwLuOjHL47Wl/view?usp=sharing Sprunki Retake . It now sounds like it is coming from the storage tanks at the back of the boiler - maybe below. We still have heating, we still have hot water (albeit at what feels like a lower flow than before, and with that noise at ful load) so it's okay for now - and with the boiler being 15 years old this year I intend to replace it in the summer unless a miracle happens or anyone here recognises the issue and can point to a quick / cheap fix!

Thanks again everyone.

thank you so much for the update, it's very helpful for a newbie like me!

 

[Johntheo5]

Is the wheezing/noise only occuring now with DHW on?, and no noises with CH on?.

 

[dunder101]

Yes, Johntheo5. That's correct - no noises with CH, only DHW - and only at full load (bath tap open fully for hot).

 

[Johntheo5]

OK, can you run that bath tap fully open again, then reduce the flowrate until the noise just stops, then measure this flowrate by letting it run into a container of a known size if available and take the exact time to the nearest second taken to fill it, you can then calculate the flowrate in LPM or whatever.

Edit: If you do carry out this test please post the DHW temperature setting on the boiler as well.

 

[dunder101]

Firstly, thank you for your help Johntheo5.

I've done this and it is 7.5 litres per minute hot water at the point there is no noise. That is about half what it should be.

This is very interesting ...

 

[Johntheo5]

Can you measure the HW temperature at this flowrate and see what the DHW temperature setting is on the boiler.
Even if its 60C the boiler is only outputting, 7.5*60*(60-18)/860, 22.0kw. (from a mains temp of 18C)

 

[dunder101]

The boiler is currently set to 60C for the DHW. I just tried to measure the temperature at the bath hot tap and it is hotter than the temperature the thermometer would register (which I believe is max 50C, therefore implying the hit water is deliver at over 50C). I think I have a different thermometer in the garage so will have another go later.

Anecdotally, I think the hot water is coming through hotter than before these problems, albeit at a slower flow rate ...

 

[Johntheo5]

At 60C DHW temp the boiler output is 22kW, if its not noisy on CH then that implies that the boiler output/heat demand on CH), is also < 22.0kW, does that sound about right, the boiler output may also be limited with parameter D.00 which you can see in the diagnostic page (only limits it on CH). Just to be sure that the noise is from the primary circulation side, maybe just shut the boiler down and open that hot tap fully to confirm no noise from the HW side even though it will now only run cold, presuming the mains water will still run through the PHEX and storage cylinders.

 

[dunder101]

Okay, so I have turned off the boiler and run the bath hot tap at full flow. Once the hot water is exhausted and it runs cold, the noise from the boiler stops. And it starts again when the boiler is turned back on and water is heated again.

I've also run test programme P1, which I think fires the boiler at full power on the CH circuit. No noise at all.

So does this point to a problem with, for example, the PHEX?

 

[Johntheo5]

Its quite possibly the PHEX, your above test might suggest fouling on the DHW side, I have seen posts of their removal and cleaning with brick? acid or similar but don't know the method.

 

[dunder101]

Thanks again Johntheo5 - I shall look at whether it's worth investigating the PHEX.i really appreciate your time.

 

[dunder101]

So the PHEX has been removed, cleaned and flushed and reinstalled. Unfortunately this made no difference, but I was worth a shot. Thank you again for your advice - I really appreciate it.