Megaflo air bubble

[fezster]

I noticed today that the pressure gauge on my incoming water supply was showing over 5 bar and creeping up fairly rapidly until it went past 6 (that's the max it goes to) and continued. The Megaflo pressure reducing valve should be 3 bar, and this is normally what the gauge shows. The only thing that was heating at the time was my Megaflo cylinder. It got to about 7 bar and then stopped. There was no water dripping from the tundish on the TPRV. However, did notice the tundish on the pressure relief valve (8 bar I believe) was passing water.

This said to me the air bubble is depleted, so recharged it as per the instructions, and it stopped all it's gurgling noises and dripping from the hot tap after about 2 hours (!). Then turned on the heating to the HW again. After 10 mins or so, came back and the pressure gauge is showing 4 bar. So much better, but still creeping up - slowly this time. It got to about 5.5 bar before the HW zone valve closed.

This implies to me the air bubble is not taking the full expansion of the hot water. I would guess that most people don't realise as the PRV passes water and all is well. I happened to have a pressure gauge fitted at some point, but most wouldn't.

But is this normal? I'd have expected the air bubble to take the full expansion? Should I look to have an external potable expansion vessel fitted at some point, as recharging the air bubble every year or so is quite annoying.

 

[Gaz the Sparky]

I am not a heating engineer so don’t quote me on this but I use to own a house with one of these fitted with the bubble. I was instructed by my regular engineer that these need to serviced once a year and part of this service replenishes the air bubble in the tank

 

[fezster]

I am not a heating engineer so don’t quote me on this but I use to own a house with one of these fitted with the bubble. I was instructed by my regular engineer that these need to serviced once a year and part of this service replenishes the air bubble in the tank

It was serviced a few months ago and the guy was reluctant to recharge the air bubble, saying I could follow the instructions on the side of the tank myself. As I'd done it before, that was fine. I don't blame him to be honest - especially as it took 2 hours on this occasion. I actually prefer not having to pay for his valuable time on this one.

 

[fezster]

N O F A !!!

Another useful contribution. You're getting the hang of this

 

[fezster]

As the megaflo is on the ground floor, opening the lowest tap as per the instructions was not regenerating the air bubble. Solution was to drain the cylinder sufficiently to allow air into the cylinder.

All sorted now and pressure does not increase and PRV does not open. Hopefully this will be useful to somebody else.

Will definitely have an expansion vessel added at the next service, as this air bubble malarkey is damn right annoying.