Hi, elderly neighbour has a Megaflo unvented CH system. Working well except he’s got a small, steady drip from the PRV on the Megaflo. Had a quick look and there’s instructions on the side of the tank to recharge it. He’s never done this, 15yrs!

I then had a go a recharging following the instructions – mains flow off to tank, lowest hot water tap on and then open valve by PRV for water to flow out the drain pipe. After a couple of mins, water was still flowing out happily.

Is this normal, how long does it take until water stops flowing and air gets in and gurgling sound?

Don’t want to make matters worse. Tried calling plumbers but understandably, they’re stacked at the min.

Cheers

It takes flippin ages and sounds like you are doing it right

(I don’t know how long it actually takes could be only ten minutes but when I’m stood waiting if feels like forevaaaaaaa)

+1

Is it gurgling now?

It can take a few minutes depending how much air is needed to recharge it.

After a couple of mins, water was still flowing out happily.

Out of where? The lowest tap or the valve (which you is sprung loaded and you are holding open?

If it’s the latter, rather than keep holding it, I tend to now put some molegrips on the valve and wedge them so that it holds the valve open. Then go and do something else!!

You have left the lower tap open haven’t you (this is where the air gets in to recharge the expansion gap).

If it’s the latter, rather than keep holing it, I tend to now put some molegrips on the valve and wedge them so that it holds the valve open. Then go and do something else!!

With a bit of care, I could normally find a balance point where the sprung valve would stay open without me having to sit there holding it!

Mine’s too strong for that – springs back shut immediately

Make sure you’re turning off the right tap. You need to isolate cold supply to the tank, otherwise it’ll just empty the local reservoir down the drain.

Water flow from the hot tap should stop almost instantly, but the gurgling will take a little longer.

Mine takes between 5-10 minutes to stop gurgling.

OP can’t reply as he’s stuck holding the valve open listening to glug, glug…… glug, glug!

Ha ha @ sharkbait!

Cool, I’ll give it another go later.

When I tried, after a few mins it was still flowing out of the tank as I held the valve open. I ‘think’ tho, that the hot tap downstairs was still flowing too … that doesn’t sound right???

Realised I hadn’t turned off the boiler, figure this would be sensible to do too?

Thanks for the help, would help appease neighbour’s mind … and hope if I can do it correctly, then the PRV may stop leaking!

Water flow from the hot tap should stop almost instantly

mine doesn’t, fwiw

I ‘think’ tho, that the hot tap downstairs was still flowing too … that doesn’t sound right???

No! Sounds it like you haven’t closed the supply to the tank – how did you do it?

If you look towards the bottom of the tank there will be the incoming supply pipe and on that will be a [black] pressure reducer and a smallish isolating valve/tap – turn this 90deg to close it. This one:

With that closed the water will stop running from the lowest hot tap after a little while (if you’ve stopped the feed into the tank there’s no longer anything pushing the hot water out)

Once you’ve done that you open the valve by the tundish and air will gurgle back into the tank.

You don’t need to turn the boiler off as the tank is full of water.

I can do it correctly, then the PRV may stop leaking!

It’s not actually ‘leaking’ (i.e. failed) as it’s doing what it’s supposed to do – allow excess water out because the air gap at the top of the tank has depleted.

Oh… I’ve had a megaflow for 9 years and have NEVER done this.

Water does let by the PRV pretty regularly but other than that, what “difference” will this process make please?

(I’ll do it no worries but am curious0

TBH I’m not entirely sure!! I guess it’s a pressure thing as the air gap is there (I think) to act as a buffer and absorb excess pressure (????)

The drip from the overflow is annoying though, especially as it’s hot water that just flowing out of the tank!
My overflow is near the front door so it can’t be left running!

AFAIA recharging the tank is pretty much the extent of ‘servicing’ as I can’t see what else they would do on an annual basis.

When the water heats up, it expands, and the purpose of the air gap is to give it somewhere to expand into, otherwise the the pressure inside the tank will increase instead. If internal pressure goes up enough, and your pressure relief valve fails to discharge properly, that would be less than ideal in safety terms.

I found that the hot water tap pressure was variable when the tank needed a recharge – it would start strong but tail off a bit.

See……. knowledge 🙂

EDIT: Actually, that was apparently massively overpressured, so not necessarily a realistic scenario. These tanks are tough, but a failure doesn’t really bear thinking about.

what “difference” will this process make please?

Peace of mind???!

Water does let by the PRV pretty regularly but other than that, what “difference” will this process make please?

For a start it’s not good for the PRV to sit slightly open. Secondly the air bubble helps maintain the system at more or less a constant pressure, instead of spiking up to the PRV release point and applying that pressure to everything connected to it. Thirdly, with the system at its maximum pressure you run the risk of turning a hot tap on and scalding water shooting out at high pressure. Apart from that though, nothing.

Hi, have had another look – you’re right, I hadn’t isolated the cylinder inlet. So, cut off mains supply to cylinder, hot tap on, and it stops flowing after 2mins, open valve by tun, and water flows out into the tun and outside.

20mins later, water still flowing out, no gurgling of air that I can hear … doesn’t sound right or can it take 20+ mins???

Thanks

At that age, the internal air baffle may have failed. It can take more than 20 minutes, but I’d expect to hear it gurgling away.

I can’t work out what you’re doing

My method (IANAMegafloEngineer):

Close isolator valve (as per pic above)

Go downstairs and open suitable hot tap – it’ll run for a couple of seconds then stop (oh, maybe that’s what flaperon meant up ^ there)

Go back to the tank and open the valve by the tundish (the one everyone talks about using molgrips for – me too)

At this point the open hot tap downstairs starts to run – let it run dry (not sure that’s truly essential but that’s what I was told to do by plumber).  I suppose this may depend on relative location of tap and tank.  My tank is a floor above the tap so has gravity on its side – still can take what feels like 5 minutes (that particular tap has quite shit flow anyway, though)

Close the hot tap

Go back to the tank and release the “tundish” valve

Re-open the isolator valve

Job done

Apologies if I’m unclear – this is what I’ve done…

1. Close isolator valve on the main water inlet to the megaflo cylinder (in the loft)

2. Run downstairs, open lowest hot tap

3. Hot water flows out for 1-2mins and then it stops

4. Leave hot water tap open

5. Back to Megaflo and turn a blue valve knob but the tun dish, and water flows out the Megaflo into tun dish

6. Keep blue valve open …

But water just kept flowing for 20mins, so I stopped and seeking guidance!

Ooooh no – I don’t think it should run into the tundish.  The valve you open on the megaflo is marked (mine anyway) “temperature & pressure relief valve”.  It’s sprung as the others said and it needs holding open (around 30-45 degrees of turn I’d guess)

Oh wait – maybe it does go via the tundish.  I forget.  Haven’t done mine for ages.

I’d get onto youtube & see what “they” say (with pictures)

Edit – thinking about it, I pretty much certain it doesn’t and shouldn’t.  Air (I THINK) is going IN via the tundish pipe

There are two relief valves on the Megaflop. Make sure you’re turning the correct one.

There are videos on YouTube which walk you through the process.

There are two relief valves on the Megaflop

Are there?

There’s only one on my two.

Right, this is mine…. Fairly self explanatory I hope.
https://photos.app.goo.gl/nP3f1JXjAe7SZ9Tz9

But water just kept flowing for 20mins, so I stopped and seeking guidance!

My guess is that your not isolating the tank.
Is it also in the loft because if not I don’t know what your isolating up there

Ooooh no – I don’t think it should run into the tundish.

I’ve just tried turning/opening the valve on mine without isolating the tank (I e. Not turning off the supply) and water ran out into the tundish.

If it’s not gurgling when you open the valve then something’s not right.

Hi, thanks for all the pointers, I’ll take some pics tomorrow as shark bait has done and that might help clarify stuff.

I agree, figure I’m not isolating the tank, plus there are 2 valves I think on this system, but if I take pics – I’d just love to get it sorted for her.

Really appreciate the help 🙂

At that age, the internal air baffle may have failed.

I’d be immensely pissed off if it had at just 15yrs old.
One of mine is 20 years old and is just fine.

So would I, just that it’s a possibility. No gurgling for me suggests that something is wrong internally, I’m pretty sure OP is following the correct procedure, unless there’s some quirk in the plumbing that makes things awkward.

I would say that Megaflo stuff comes with a very long warranty, but that is dependent on an annual service being carried out, which is reasonable, TBH.

@Aus
I’ve just watched a video re “servicing” (almost laughable) and there were indeed two valves, a blue T&P valve and the black non-return valve.
On both my tanks (different houses and different installers) I don’t seem to have a T&P valve (I’ll check), just the non-return valve as in the photo I shared.
For nearly 20 years I’ve recharged the airgap using the non-return valve.

The blue T&P valve in the video was further down the tank and being used to drain the tank down.
Sounds like that’s what you were doing.
The black non-return valve is on a pipe that connects near the top of the tank (as seen in my pic)

lowest hot water tap on and then open valve by PRV for water to flow out the drain pipe.

Just reread your original post and saw this. I think you’re opening the wrong valve.

My money is on the blue valve being connected further down, which would obviously allow me all the water above that connection to drain out of the tank to that point!

The valve you’re looking for is connected no more than about 30cm down from the top of the tank and will obviously only allow a much smaller amount of water to run out.

The Valve on the tank is the Temperature/Pressure relief valve (TPR).
The other valve is just a pressure relief valve (PRV) for the cold water inlet.
The lower (PRV) valve on sharkbaits second pic is the round black knob just above the circled valve lever. It’s not a non return valve. The PRV’s main function is to protect the cylinder in the event of a failure of the pressure reducing valve. The TPR valve works in the same way but it also has a thermocouple built in for releasing water if the temperature gets too high.

OP, is there an expansion vessel external to the tank? Megaflo cylinders have a dip tube in the top of the cylinder which can be removed to give extra capacity by removing the expansion gap. If that has been done then there will be an external (white) vessel installed. This could explain why you still have water coming out. When you recharge a Megaflow normally, with dip tube installed, its the water level reaching the bottom of the dip tube (200mm -300mm approx iirc) that gurgles when recharging it. All that is happening is that you are creating an air space above the water in the tank which allows expansion of the water when it is heated up.

Hi, and again, thanks for the support. Sorry, couldn’t pop in yesterday to look and get pics, but I’ll be going in tomorrow so will do that then.

Sharkbait (and others) – think you’re right. From memory there’s a blue valve, halfway down the tank, on the balance valve near the tun dish, I’ve been turning this and I think you’re right that I’m just emptying the tank.

There is, I think, a ‘pull lever’ type valve release on the the pipe that enters/exits the tank highest up, so figure I should be pulling this.

Also, to isolate the tank, the isolator I’ve been turning is the lowest placed pipe feed/exit to the tank, and wonder if this is the drain and not the feed. Presumably if I turn the mains stopcock off, this will do the isolating job ok?

Still trying to get a plumber in for her, but mostly, none return my call, and none interested!

Will update tomorrow with pics, but I (and she) really appreciate the help.

Presumably if I turn the mains stopcock off, this will do the isolating job ok?

Yep

There is, I think, a ‘pull lever’ type valve release on the the pipe that enters/exits the tank highest up, so figure I should be pulling this.

No idea about this – does the pipe it’s on feed into the tundish?

Still trying to get a plumber in for her, but mostly, none return my call, and none interested!

Once you figure it out you’ll realise just how simple it [should be]/is!!

I can’t help with the actual process but would add that you might need to check the PRV still works properly. Our Megaflo had been in for 8 years without a service/recharge, eventually we discovered water coming from the PRV. It had been leaking for quite some time and limescale had built up and was holding the valve open (we live in a very hard water area).

Behaviour wise – we’d been seeing hot water pressure drop off after 20-30 seconds, and some weird behaviour in one shower where it would suddenly let a load of water go (almost as if there was an airlock somewhere that had let go). Once the system was recharged these problems went away.

@sharbait – yep, the lever-pull valve feeds into the tun dish, and I think from memory, when I pulled it, hot water released.

tonyd – the PRV unit has limescale around it so fear it might too be rather limescaled up

OK, so I’ve just been round again, and suspect turning off the mains water is not the obvious stopcock, there seem to be 2. So with both these off, the low hot water tap ran out after 1-2mins. Went up to the cylinder and opened the lever valve uppermost on the cylinder – I think this feeds hot water to the tun dish – as I opened it, a brief whoosh of air momentarily, no water drains out to the tun dish, no gurgling, no further intakes of air.

Shut the lever valve, turned mains back on, hot water spluttered out the low tap for 30secs and then steady flow.

I’m guessing that it’s not fully recharging?

But thankfully, have eventually got a plumber who’ll come next week as the drip is is still there.

Thanks for all the help.

Dripping from the large central black valve …

The blue knob seems to simply release cold water into the tun dish, so not the pressure valve?

This is the uppermost lever pull valve … pressure release valve?

I thought this was the isolating valve, lowest cold pipe …

I’m at a loss. It looks a little strange but maybe mine are set up very simply!

I think you’re right in the location of the cold supply to the tank and the lever valve (although different to mine) looks to the right also.

The insulated pipe next to the immersion is either the feed from, or return to, the boiler – the other one seems to be further up the tank (with the red bleed valve?) ….. mine are next to each other at the bottom.

I’m guessing that’s a pretty old tank as mine have a sleeker looking immersion unit. It’s also quite a small tank which confused me for a minute as the lever valve looked too low, but it’s not.

I don’t have any more advise – sounds like you’ve done the correct procedure so maybe there’s a failed valve.

IANAP obvs!

This is mine. On the left is the water in, you can see the handle to turn off the water.
Once off I open the lowest hot water tap and turn the black knob with blue top. (This is the bit that drips when I do this procedure).
The hot water tap will run for a bit then slow to a trickle. With the blue knob held open it’ll start to gargle, for a long while. Like 15 minutes. If it’s not glugging something isn’t turned off.
One it stops release to blue top and turn on water. If you have a mole wrench you can adjust it to hold the blue topped knob then prop it open.