Megaflo problem... and is it time for a new heating system?

RainbowLaura

Hi everyone,

For the last few weeks my Megaflo water cylinder has been dripping cold water through the tundish whenever the water is heating up. I followed the instructions to recharge the air bubble, twice, but it's made no difference. I had a G3 qualified engineer come and look at it the other day who tried re-charging the red expansion vessel, although the pressure has always been between 1-2 bars. He said if that didn't work then we would need to replace the red vessel. Unfortunately, although the pressure gauge is still 1-2 bars, the tundish is still dripping away

He didn't say how much it might cost to replace the vessel. What sort of range would be reasonable?

The main concern is that the heating system is 17 years old and this year we have had to have a new circuit board in the boiler, a new thermostat on the Megaflo, a new motorised valve and some leaking pipework seen to

Now we've spent such a lot of money on it I really don't want to scrap the lot and buy a new system... but on the other hand, I don't want to spend another load of cash only for something else to break in the near future (if there's anything in the bloody thing left to break!!!), or if the replacement vessel still doesn't solve the problem. Should this be the point at which I go for the combi and just get rid of the lot? I am getting so sick of all the repairs needed on this system. If we'd had one large bill then we wouldn't have thought twice about scrapping it and starting with a new one, but the problem is that all the failures have been happening one by one

Thoughts would be greatly appreciated.

Owain_Moneysaver

Is the red expansion vessel for the Megaflo (hot water) or is it for the primary circuit (boiler and radiators)?

If the Megaflo is dripping through the tundish that suggests to me the pressure/temperature relief valve is letting through and may need to be replaced.

If the primary circuit is dripping through its tundish then the boiler pressure gauge reading would be dropping, but that would have no effect on the hot water pressure in the Megaflo.

Presumably by Megaflo and bubble you mean this procedure:

http://www.fixmyplumbing.org/fixing/reinstating-the-air-bubble-in-a-megaflo-cylinder-2/

whether it actually works does depend sometimes on the height of the cylinder relative to the taps you open, as air has to get into the Megaflo to reform the bubble.

New expansion vessel £30 - £50 plus fitting
https://www.screwfix.com/c/heating-plumbing/expansion-vessels/cat830984

fezster

The red expansion vessel will most likely be for your heating system, not for your megaflo. The megaflo has an internal air bubble, as you already said you tried to recharge. You *can* fit an external expansion vessel, but it has to be suitable for potable water and is usually coloured white or blue to differentiate it from the red expansion vessels used for sealed heating systems.

First things first - how did you try and recharge the air bubble? I recently had trouble recharging mine and found I had to drain roughly 30% of the cylinder to allow the air bubble to be formed, because my lowest tap was above the TPRV on the side of the cylinder (often a problem with cylinders located on the ground floor). If for some reason the air bubble cannot be replenished, you can have an external expansion vessel fitted. Roughly £40 to purchase and another £60 to have it fitted. It's also possible the TPRV is simply faulty and is therefore passing water into the tundish, or it could be your PRV, but I suspect this is not the case.

If the red expansion vessel is indeed for your heating system, I'd question your G3 qualified engineers competency to be working on an unvented system!

RainbowLaura

Both very interesting and helpful responses, thank you.

How do I confirm whether the red vessel is to do with the heating or the Megaflo?

The top of the tundish that's dripping can (just about) be seen at the very bottom of my photo, to the right.

The cylinder says to open the nearest hot tap, which is in my bathroom on the first floor of my house. However, I'm now wondering if I should try doing it with a ground floor tap?

Definitely wondering if we should get a second opinion anyway!

Alex1983

The red vessel is definitely for the heating system not the unvented, you can see it’s connected to the heating systems pressure gauge.

If your definitely recharging the bubble correctly then I’d suspect the combination valve, the brass component in the bottom centre ish of the picture. I’ve never had a megaflow not recharge it’s bubble but if for some unlikely reson it had failed most megaflows come with long warranties, some 25yrs.

fezster

RainbowLaura wrote: »

The cylinder says to open the nearest hot tap

No, it should be the "lowest hot tap". Watch this video for reference:

https://youtu.be/Cpl1ZPvhaYY

RainbowLaura

Thanks all. I tried doing it with the kitchen tap last night and touch wood, so far so good!!

However, I've noticed something else!

The motorised valve we had replaced a few weeks ago looked like this, and had done for as long as I can remember:



I always assumed there must have been some sort of leak in there long before we moved in, and often checked the area for dampness and never found any. Unfortunately, in my fiddling about in the airing cupboard I noticed that the new valve has a small limescale stain on it in the same place! Which suggests that something is still going on. It's directly below a red lever/valve, as pictured (after I cleaned the small new stain off):



As you can see, other limescale stains are visible around the red valve and on the side of the cylinder. Is this something to worry about? Again, I've checked the area for dampness and can find nothing at all...

Either way, won't be having that G3 guy back as he didn't seem interested in the re-charging of the air bubble at all, which seems to be the very most basic thing on these Megaflo systems! Not impressed!

Thanks so much for your help guys, I'm really grateful.