Megaflo Loud Vibration When Drawing Hot Water

Hi,

I have an issue and it is somewhat intermittent whereby when hot water is drawn from my UV Megaflo, it makes a very loud vibration. The pipes can be seen moving slightly when this happens if you zoom on the video.

The external EV has been checked and it's set to 3 bar. Previously it was 1 bar but it made no difference to the noise. This cylinder does have the internal bubble but this has started to break down and hence the external EV.

The inlet valve and pressure reducing valve have been replaced already and the issue persists. 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 Non return valve (single check on top of cylinder) or something within the cylinder. 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 pressure relief valve, but I can't think of any reason why it would do this. No water residue in tundish.

Thanks in advance.

Did you recharge the air bubble since the noise started even though you have a external EV?.

You need to see where the noise it being generated, that actually sounds like the noise the spring in the Pressure Reducing Valve (PRV) makes, rather than an EV noise.

Hold the combination valve and try to re-create it, it will be pretty obvious if it's the PRV. I know you've replaced the PRV but humour me

Madrab said:

You need to see where the noise it being generated, that actually sounds like the noise the spring in the Pressure Reducing Valve (PRV) makes, rather than an EV noise.

Hold the combination valve and try to re-create it, it will be pretty obvious if it's the PRV. I know you've replaced the PRV but humour me

Click to expand...

Surely not!, wasn't this the one that replaced the "wrong" caleffi combination set?.

Johntheo5 said:

Did you recharge the air bubble since the noise started even though you have a external EV?.

Click to expand...

Yes this was completed even though it's non existent.

Madrab said:

You need to see where the noise it being generated, that actually sounds like the noise the spring in the Pressure Reducing Valve (PRV) makes, rather than an EV noise.

Hold the combination valve and try to re-create it, it will be pretty obvious if it's the PRV. I know you've replaced the PRV but humour me

Click to expand...

It is my intention to try and feel what might be causing this when reproducing it. However, it doesn't happen every time. It is sporadic. The previous Caleffe block was replaced due to this and a genuine Baxi part was fitted but the issue persists.

Johntheo5 said:

Surely not!, wasn't this the one that replaced the "wrong" caleffi combination set?.

Click to expand...

Yes it was.

What about getting a PG installed somewhere and become the first in history to install a pressure gauge on a unvented cylinder?.

Johntheo5 said:

What about getting a PG installed somewhere and become the first in history to install a pressure gauge on a unvented cylinder?.

Click to expand...

I have had this suggestion previously... Where exactly would you install a PG or multiple PG's? To me it's another point that could leak but I see the fault finding benefit.

steveoelliott said:

I have had this suggestion previously... Where exactly would you install a PG or multiple PG's? To me it's another point that could leak but I see the fault finding benefit.

Click to expand...

On a T piece with a isolating lever valve, just before where the EV is (copper?) piped into the cold feed.

Hi there,

Did you ever manage to fix this? Mine is making exactly the same noise!

We are remodelling our top floor and had the tank moved from one cupboard to another and every since its moved its been making the exact same noise as your video when we draw hot water.

The installer keeps on coming over and messing around with it, but to no avail, and i'm at a loss now and trying to search forums for people who have had similar issues.

Many thanks in advance!

Well... I went through a bit of a process. Replaced the inlet and pressure reducing valve. It seemed to fix it initially but the noise returned within weeks. Mine is a Megaflow and they have an airgap at the top which gets recharged when drained. My airgap has already started to break down so I also have an external expansion vessel.

I ended up replacing the EV as a sanity check and set the pressure to 2.8 bar. I deliberately did it a bit less than 3 bar as I suspected the pressure in the EV was causing the noise when it discharged water. The noise however continued. I left it for several months and told everybody to open the hot tap slowly for 15 seconds after the heating cycle.

Anyway, over time it disappeared and now I have no issue at all. What I actually suspect is the pressure inside the EV has dropped to a "correct" pressure. The pressure in the EV is supposed to be more or less equal to the incoming mains pressure. Therefore I would be minded as a test to try lowing the pre charge pressure in your EV by ~0.5 bar or so. You need to drain the cylinder at least partially to do this but videos available online etc.

I had also considered installing a ball valve on the pipe from the EV and having it partially closed (technically against regs and dangerous) but my thoughts were water does not expand suddenly and this would reduce the flow. However, I never needed to do this.