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]

  On 16/10/2024 at 21:47, John Carroll said:

Get a pressure gauge installed.

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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, 2024 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]

  On 17/10/2024 at 11:44, 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.

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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]

  On 18/10/2024 at 12:46, 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).

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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]

  On 18/10/2024 at 17:12, 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.

 

 

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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]

  On 18/10/2024 at 19:34, 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.

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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, 2024 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.

[John Carroll]

Don't know if new cylinder is installed but just for interest, OSO technical inform that its cylinders do not have a baffle so removing the dip tube and installing a EV to give that ~ extra 20/25% extra capacity does not leave something to bang about inside.

[Doug Tag]

Have you had this fixed yet? 
 

If not adjust your pressure vessel to 0.2bar below your dynamic pressure of your cold supply to the cylinder. 
 

Most of the time those pressure vessels come charged to as much as 3 bar. 
 

At a guess 1Bar would probably sort it but the proper way to adjust it is as per above.
 

99% if the time noise problems like this is a pressure vessel problem I’ve fixed countless systems like this.
 

Anyway hope this helps 👍

 

step by step,

1) check dynamic pressure on cold supply to the cylinder 

2)isolate the cold supply to the cylinder and run off the pressure by opening a hot tap

3)check the pressure on the pressure vessel through the Schrader valve

4)Reduce the pressure in the pressure vessel to 0.2 Bar below the dynamic pressure by depressing the pin in the  Schrader valve

5)Open the cold supply back up and run the hot taps to remove air from the system 

6) turn the hot water on for an hr or until the cylinder is suitably heated up

7) open hot tap with crossed finger and  hopefully steps 1-6 have to been a waste of time 😂👍 

 

good luck but I’m optimistic 

[Doug Tag]

  On 08/09/2024 at 08:27, steveoelliott said:

Hi,

 

I have noticed that when a hot tap is opened for the first time after a heating cycle (in this case a bath tap), the water flows for a couple of seconds and then there is a very loud noise as can be heard in the video.

 

Any ideas what it may be? The EV was recently checked and pressure increased from 1 to 3 bar per instructions but notably it did this before. I just at that time didn't know the trigger. It hasn't always done this however, probably the last couple of months or so.

 

Thank you.

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Added my answer hope it helps 

[steveoelliott]

  On 01/02/2025 at 19:08, Doug Tag said:

Have you had this fixed yet? 
 

If not adjust your pressure vessel to 0.2bar below your dynamic pressure of your cold supply to the cylinder. 
 

Most of the time those pressure vessels come charged to as much as 3 bar. 
 

At a guess 1Bar would probably sort it but the proper way to adjust it is as per above.
 

99% if the time noise problems like this is a pressure vessel problem I’ve fixed countless systems like this.
 

Anyway hope this helps 👍

 

step by step,

1) check dynamic pressure on cold supply to the cylinder 

2)isolate the cold supply to the cylinder and run off the pressure by opening a hot tap

3)check the pressure on the pressure vessel through the Schrader valve

4)Reduce the pressure in the pressure vessel to 0.2 Bar below the dynamic pressure by depressing the pin in the  Schrader valve

5)Open the cold supply back up and run the hot taps to remove air from the system 

6) turn the hot water on for an hr or until the cylinder is suitably heated up

7) open hot tap with crossed finger and  hopefully steps 1-6 have to been a waste of time 😂👍 

 

good luck but I’m optimistic 

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Hi @Doug Tag

So I will be swapping the cylinder at some point. However, we (my plumber did the work) did replace the EV and I set the pressure to 2.8 Bar before giving him the EV to install. The issue persisted. The dynamic pressure varies from 2-3 bar here. The EV we took off was at 1.95 bar when checked.

 

The plumber also removed the NRV on the hot outlet from the top of the cylinder.

 

The issue persisted so that I think rules out the EV. In addition, I am even able to replicate the noise with the inlet valve to the cylinder closed upon opening the taps. This now seems to happen every time a tap is opened but to a lesser degree following the first time after the heating cycle.

 

I have heard elsewhere that the issue is likely to be internal to the cylinder, i.e. something come adrift or the old broken up baffle causing issues.

Edited February 4 by steveoelliott

[John Carroll]

You could/may still have a air bubble in the Megaflo in which the water level will rise & fall a bit especially with fluctuating dynamic pressure which can cause movement/noise  of (if) broken baffle bits. If you remove the HW outlet pipe it should be relatively easy to drill even a pin hole sized hole in the dip tube which will very quickly destroy the air bubble, you then have a full cylinder of water with virtually no movement as it will all happen in the EV and just might stop that noise.

[steveoelliott]

  On 09/02/2025 at 15:34, John Carroll said:

You could/may still have a air bubble in the Megaflo in which the water level will rise & fall a bit especially with fluctuating dynamic pressure which can cause movement/noise  of (if) broken baffle bits. If you remove the HW outlet pipe it should be relatively easy to drill even a pin hole sized hole in the dip tube which will very quickly destroy the air bubble, you then have a full cylinder of water with virtually no movement as it will all happen in the EV and just might stop that noise.

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Whatever it is seems to change... sometimes it's not there at all, other times it's very quiet and other times it's loud like some of the videos on here.