Megaflo UVC - Very Loud Noise When Hot Tap Opened First Time After Heating Cycle

[steveoelliott]

A week on, this hasn't so far got any worse but it doesn't happen every time the hot water in drawn.

 

For the purposes of testing, I always use the bath hot tap, opened fully. As an example, I drew hot water right after the heating cycle for ~10 seconds, no noise. Repeated the process after 30 seconds, no noise. On the third go, it made the noise a few seconds after drawing hot water.

 

This to me rules out expansion and or pressure. Since they would be much higher / worse after the initial heat cycle.

 

Baxi and my own plumber are at a loss to what this might be.

[John Carroll]

Get a pressure gauge installed.

[steveoelliott]

14 hours ago, John Carroll said:

Get a pressure gauge installed.

At which location? Between the reducing valve and EV or on the hot water outlet? I can't seem to find a pressure gauge that doesn't come as part of a PRV block.

Edited October 17 by steveoelliott

[steveoelliott]

Right, so today I did a new test. Shut off the incoming feed into the cylinder and was able to reproduce the problem. This in my opinion removed the possibility of anything on the inlet side.

[John Carroll]

23 hours ago, steveoelliott said:

At which location? Between the reducing valve and EV or on the hot water outlet? I can't seem to find a pressure gauge that doesn't come as part of a PRV block.

Ideally,on the feed  downstream of the expansion relief valve, would need a T with a isolating valve and the PG on the end of the T.

[Nickfromwales]

Is the non return on the UVC hot outlet a single check or double check? 
I’d look at that next as these tend to be quiet with lots of flow/pressure and noisy with lower values.

May be the ‘groan’ off that tbh.

 

The installer has done a good job here, so I think it’ll be down to component failure vs misadventure, so if there’s a secondary pressure reducing valve at the cold mains stopcock then try fitting a straight coupler in place of that NRV and see if that kills the issue. 
A simple additional ‘process of elimination’ there imo, and worth trying. Just remember to double check that the secondary PRedV is functional before committing to a day of testing. 
(FYI the primary PRedV will be the control group at the UVC).

[steveoelliott]

4 hours ago, Nickfromwales said:

Is the non return on the UVC hot outlet a single check or double check? 
I’d look at that next as these tend to be quiet with lots of flow/pressure and noisy with lower values.

May be the ‘groan’ off that tbh.

 

The installer has done a good job here, so I think it’ll be down to component failure vs misadventure, so if there’s a secondary pressure reducing valve at the cold mains stopcock then try fitting a straight coupler in place of that NRV and see if that kills the issue. 
A simple additional ‘process of elimination’ there imo, and worth trying. Just remember to double check that the secondary PRedV is functional before committing to a day of testing. 
(FYI the primary PRedV will be the control group at the UVC).

How would I check if it is a single vs double check? Excuse my ignorance. You make a good suggestion re the removal of the NRV. An easy thing to try. The incoming PRV on the main never goes much above 2.2 bar dynamic even wide open so that's the most mains pressure we get here. I guess it may occasionally go higher but I've never seen it.

 

 

[steveoelliott]

On another point, since running the test I carried out yesterday with the inlet valve shut, I cannot reproduce the noise once again. I imagine it will rear it's head again in time, but isn't that strange! I can't see how the 10-15 liters of water that got drained out of this whilst testing made any difference. The only thing I wonder is if something is adrift in the tank and moving around until a point it gets stuck / lodged. Pure speculation of course.

[Nickfromwales]

2 hours ago, steveoelliott said:

How would I check if it is a single vs double check? Excuse my ignorance. You make a good suggestion re the removal of the NRV. An easy thing to try. The incoming PRV on the main never goes much above 2.2 bar dynamic even wide open so that's the most mains pressure we get here. I guess it may occasionally go higher but I've never seen it.

 

 

A single check will be quite short, a double check longer and with a hex nut for service (in the majority of cases). Defo try what I suggest and eliminate that is my 2 cents.

[steveoelliott]

1 hour ago, Nickfromwales said:

A single check will be quite short, a double check longer and with a hex nut for service (in the majority of cases). Defo try what I suggest and eliminate that is my 2 cents.

Thanks… That said, it is strange that after the test I did yesterday, I can no longer reproduce the issue.

[steveoelliott]

Well, I can firstly confirm the cylinder has a single check valve and not a double. @Nickfromwales

 

I have once again been able to reproduce this issue and I am confident the external EV plays no part in this. When this video was taken a significant amount of hot water had been used since the last heating cycle and testament to this fact is the EV was cold to the touch as was the pipe between that and the cylinder.

 

I am leaning towards thinking either a dodgy NRV or something within the cylinder. Interestingly, this time the noise was much louder and echo's. Any feedback welcomed. I've decided the next course of action is the NRV. Interestingly, if you watch the video zoomed in you can see the tundish and pipe around it vibrate with the noise. I am even curious if this could be the PRV but I can't think of any reason why it would do this. No water residue in tundish.

Edited November 7 by steveoelliott

[steveoelliott]

I’ve decided that I’m going to remove the NRV on the top of the cylinder and replace the T&P valve whilst I have the plumber out. 
 

After that the only part not replaced will be the EV.

[steveoelliott]

OK, so my plumber came today and for the first time I reproduced it with him in the loft next to the cylinder.

 

I had him out to replace the NRV, T&P and EV. Figured I'd make sure everything had been done but after hearing the noise he told me it is definitely coming from inside the cylinder. On another group a plumber suggested that the breakup of the baffle can cause this noise as it catches / releases. Anyway, I've contacted Baxi to get a replacement.