Megaflow recharge interval

4 Sep 2009
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United Kingdom
16/17 YO system. In 2013 the recharge interval started to get very short, 1-2 months. Dripping from the tundish was the indicator. As per manual recharging the bubble fixed the problem.

This was also accompanied by a squeal from the prv.

Prv was replaced in August 2013 and then the frequent recharge also stopped. First was in the spring but Since then I'm back to doing this every 2 months.

When the drip occurs there's also a noticble pressure in the hot water system, you can feel it as you slowly turn on a tap.

I guess the pvr was not the cause, just a side effect.

Google tells me I shouldn't be doing this so frequently so putting it out there for some welcome advice.
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You may have something back feeding mains pressure into the hot water system, normally its where the hot and cold meet such as a shower valve or monobloc kitchen mixer, turn off the feed to the cylinder and see if you still have water coming out the hot taps.
Bingo, I do.

Anyway to work out which tap it could be? All of them are mono block.
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It won't be a new tap that have separate outlets within one tap ( water regs) old taps and showers/ bath mixers that normally the problem
In trying to isolate one of the taps the isolation valve springs a leak.

Wondered if thats the faulty tap so building pressure behind the valve, ie the wrong side? or am I just getting crappy luck and have found another problem.

Regardless I thought I'd try and drain the pipes so I could check that.

The megaflow stop cock is off and I turned the mains cold off. Which in the past stops all the taps.

Cold is stopped, but hot is running fine. Should I just open all the hot taps and drain the cylinder or will that cause me a bigger issue when it re-fills?

G/f just pointed out we have BG cover & I should stop messing around and call them. She's probably right.
well that escalated quickly.

fixed the isolation valve, eventually. involved a mad dash to screwfix, some cuprofit connectors & lots of swearing. Cant say they fill me w/ confidence but seem leak free at the moment. And after that it wasn't even that tap.

No closer to finding the mixer culprit. Although I suspect the bath shower mixer. g/f told me this morning that she often gets a cold shower first thing until she messes with the lever. Wondered if its dripping cold water into the hot overnight.

Tried experimenting with it, leaving it partially open etc, all the way to hot, all the way to cold. Still get a slight dribble from one of the hot taps.
Most of the time for me when I've had this problem it ends up being an old shower (or occasionally a new one when someone has lost one of the non-return valves!).
Not seen this before, why does the cylinder back fill? It's under mains pressure and if your not drawing any off it will fill only in the feed connection right?

This could only happen if it's not balanced supply's ???
When a Megaflo is installed there is a 22mm branch near the PRV, this is the "Balanced Cold" connection, however many installers neglect to use this port and so the Cold taps are at higher pressure than the "controlled Hot Water" the first place I would look is any Shower mixing valves - it could be scale build up in the hot side non return valve! ;)
Yeh I was thinking that last night that's the only way this could happen" not balanced supply's.

Cold water coming back up the hot in to the cylinder.

Problem is a lot of these cylinder are not fitted correctly with a balancing vlv.

God knows why they don't just fit a erasure reducing vlv at the cold mains stop tap. So everything is set to that same pressure.
Baffle plate has possibly 'flipped' within megaflo causing the air gap to deplete @ a faster rate , also increasing hot water temp can aid in loss of air gap.

Look into having a remote expansion vessel fitted.

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