Any suggestions on what's up with Megaflow?

housebuyer143

So, I have weepage from the tundra, but not always. Sometimes it's bone dry, others is wet to touch. The water is cold. 

The engineer changed the PRV and the other release value and it seemed to stop the leaking for 6 weeks, but now it's back. I did the air gap 2 months after her came and it did need redoing. I probably had to wait 3-5 mins for it to replenish, so not that bad but air was lost.

I replenished the air gap on Tuesday and then did it again yesterday after noticing that it was wet and the air gap is still there (it gurgled 3 times and then stopped). I feel like it's wet while the tank is heating and maybe an hour afterwards.

They want to come back and fit an expansion vessel but feels like they just don't know what else to do as they replaced the only parts they would have in the line of investigation. 

Any suggestions why it would be weeping if the air gap hasn't disappeared?

Rodders53

Mixer taps letting by and over-pressurising the HW side, perhaps? 
IF the cold pressure to such taps is in excess of the PRV setting for the cold water into the Megaflo... 
Then when the HW is heated up it exceeds the over-pressure valve setting?

OR a faulty from new PRV letting by. 
Or the overpressure valve not reseating (again faulty from new).

A pressure vessel external won't fix any of the faults I have listed.

I'm not a G3 qualified plumber; which anyone working on such cylinders must be.

housebuyer143

Rodders53 said:

Mixer taps letting by and over-pressurising the HW side, perhaps? 
IF the cold pressure to such taps is in excess of the PRV setting for the cold water into the Megaflo... 
Then when the HW is heated up it exceeds the over-pressure valve setting?

OR a faulty from new PRV letting by. 
Or the overpressure valve not reseating (again faulty from new).

A pressure vessel external won't fix any of the faults I have listed.

I'm not a G3 qualified plumber; which anyone working on such cylinders must be.

@Rodders53

We do have very high cold water pressure. We have to turn all taps off very tight or they drip and plumbers have mentioned it before as well. 

We have two mixer taps in the house. One is brand new in the kitchen - we only ever use it on cold fully or hot fully and the mixer in the bathroom is mostly hot with a tiny turn of cold because that's all it needs. Could it backfill in these circumstances? If so, how can I test which is the culprit?

Assuming these new PRV parts are not faulty, and they install an external expansion, will it not just fill with water as well? I don't want to have to re-air it all the time as well.

Rodders53

I'm not a plumber but these are things the G3 plumber should be considering.

Anything can go faulty.  Good quality devices have 'non return valves' in them to prevent back flow - but they can go faulty.
Any device can be faulty from new, or develop an early fault.  It's not that common but not that rare either.

A plumber worth his salt will know how to check for such 'passing' (and also the kit to measure pressures of both H & C systems).  {A whole house PRV may be needed ideally to balance H & C in an ideal world ?} 

I'd isolate the cold to such a tap.  Disconnect the cold pipe to the tap (after the isolator) and run the tap in mid-position (both H & C equal)... if water comes out that cold pipe (into a bucket under it) it's passing from the hot side... it'll be warm/hot, too!

The megaflow bubble will be no longer needed when an external pressure vessel is fitted  - it has a bladder inside to absorb the increased pressure / water volume due to heating expansion.  Repressurising is part of the annual service, when needed.  Not usually advised for DIY but for G3 plumbers.

housebuyer143

Rodders53 said:

I'm not a plumber but these are things the G3 plumber should be considering.

Anything can go faulty.  Good quality devices have 'non return valves' in them to prevent back flow - but they can go faulty.
Any device can be faulty from new, or develop an early fault.  It's not that common but not that rare either.

A plumber worth his salt will know how to check for such 'passing' (and also the kit to measure pressures of both H & C systems).  {A whole house PRV may be needed ideally to balance H & C in an ideal world ?} 

I'd isolate the cold to such a tap.  Disconnect the cold pipe to the tap (after the isolator) and run the tap in mid-position (both H & C equal)... if water comes out that cold pipe (into a bucket under it) it's passing from the hot side... it'll be warm/hot, too!

The megaflow bubble will be no longer needed when an external pressure vessel is fitted  - it has a bladder inside to absorb the increased pressure / water volume due to heating expansion.  Repressurising is part of the annual service, when needed.  Not usually advised for DIY but for G3 plumbers.

@Rodders53

Thanks, I will have a look into the taps and see if that happens. It's frustrating because I mentioned backfilling to the engineer and he says "it won't be that... or probably not" and processed to just dismiss the idea. Not one of the 3 engineers have tested the pressure on anything when here.
I vaguely remember the second engineer mentioning about maybe a second PRV and maybe he meant on the incoming cold main as you suggested. 

Refilling the air gap in the megaflow - I was shown by the megaflow engineer on two occasions so I'm confident with that, but once they start putting in external vessels my confidence in doing it decreases and I don't want to mess with things I don't know how to do.
Do you think though, if backfilling is an issue that the new external expansion will have the same problem as the internal expansion, in that it constantly needs the air gap recharging? That's probably worse than the current situation if so because I can't call someone out up recharge it every month or two.

Ibrahim5

I have had a Megaflo for over 20 years. Our cold water comes in at about 6 bar. The Megaflo is at 3 bar for the hot water. The G3 plumber who installed it didn't bother fitting the cold supply to the balance valve. A couple of years ago I fitted some kitchen taps with flexible hoses that said max 5 bar so I popped a PRV in on the cold. I liked it so I popped another PRV in for the cold supply next to the Megaflo which was easier than connecting it to the balancing valve. Must say I love the controlled water pressure on the cold side now. The taps work really nicely and you don't have to battle to turn the cold off. I replaced a fair few cold taps over the years damaged by the pressure. It wasn't easy to fit a whole house PRV but I have the same effect now. Wish I'd have done it years ago. I think pressure reducing valves will also save money on water saving. You get much more controlled flow of water. I would look into getting pressure control on the cold.

housebuyer143

Ibrahim5 said:

I have had a Megaflo for over 20 years. Our cold water comes in at about 6 bar. The Megaflo is at 3 bar for the hot water. The G3 plumber who installed it didn't bother fitting the cold supply to the balance valve. A couple of years ago I fitted some kitchen taps with flexible hoses that said max 5 bar so I popped a PRV in on the cold. I liked it so I popped another PRV in for the cold supply next to the Megaflo which was easier than connecting it to the balancing valve. Must say I love the controlled water pressure on the cold side now. The taps work really nicely and you don't have to battle to turn the cold off. I replaced a fair few cold taps over the years damaged by the pressure. It wasn't easy to fit a whole house PRV but I have the same effect now. Wish I'd have done it years ago. I think pressure reducing valves will also save money on water saving. You get much more controlled flow of water. I would look into getting pressure control on the cold.

Thank you. We love the pressure for showers, but I suppose how high is too high. The taps drip if not turned off tight, the toilets refill insanely loud etc. 

I might get someone to look at a PRV on the incoming cold or at least ask megaflow engineers to check this before installing an external vessel.

Rodders53

Magaflo cylinders have a plastic 'baffle plate' between the water and air --- designed to reduce the air being absorbed into the water as fast.  I have an Oso HW cylinder that has no such baffle plate, but a 'dip stick/tube' into the water for HW draw off (the Megaflo possibly has similar).

It's the air being absorbed into the hot water over time that needs the bubble refilling.  If the bubble is too small to absorb the water expansion (pressure increase) the the pressure relief valve operates and vents water to the tundish.  
Similarly, if the boiler and/or immersion overheat the water an overtemperature valve will vent super hot water down the tundish.
The incoming PRV also incorporates an overpressure relief valve and non-return valve,  Set higher than the main tank PRV/overtemp valve set.  8 bar I believe on Megaflos.

AIUI the bubble is replenished by operating the PRV on the tank to let air in (same as on my OSO) .... that is one area than is likely to not re-seat properly and then pass water as it expands even at lower than normal pressure. Just need a bit or scale in hard water areas to cause problems. 

IF an external vessel is introduce the Oso instructions are to remove the dip tube and then have no air bubble. I'd expect the Megaflo to be the same?  (Find the manuals online to read).  It gives a larger hot water storage as a bonus. 

BUT if the valves are leaking or cold water at higher pressure is back-feeding into the hot causing a PRV to operate the same dripping at the tundish will happen.

I believe that some makes of HW cylinders have a pressure gauge on the inlet set (mine hasn't) or elsewhere on the HW side. e.g. on an external pressure vessel install (mine in my last home didn't, though).  I don't know how practical they are to be retrofitted and if they give any long term issues?

Also have a look at other forums (DIY / Plumbing) for your issue in case someone who is a tradesman rather than amateur like me has any firmer ideas.

housebuyer143

Rodders53 said:

Magaflo cylinders have a plastic 'baffle plate' between the water and air --- designed to reduce the air being absorbed into the water as fast.  I have an Oso HW cylinder that has no such baffle plate, but a 'dip stick/tube' into the water for HW draw off (the Megaflo possibly has similar).

It's the air being absorbed into the hot water over time that needs the bubble refilling.  If the bubble is too small to absorb the water expansion (pressure increase) the the pressure relief valve operates and vents water to the tundish.  
Similarly, if the boiler and/or immersion overheat the water an overtemperature valve will vent super hot water down the tundish.
The incoming PRV also incorporates an overpressure relief valve and non-return valve,  Set higher than the main tank PRV/overtemp valve set.  8 bar I believe on Megaflos.

AIUI the bubble is replenished by operating the PRV on the tank to let air in (same as on my OSO) .... that is one area than is likely to not re-seat properly and then pass water as it expands even at lower than normal pressure. Just need a bit or scale in hard water areas to cause problems. 

IF an external vessel is introduce the Oso instructions are to remove the dip tube and then have no air bubble. I'd expect the Megaflo to be the same?  (Find the manuals online to read).  It gives a larger hot water storage as a bonus. 

BUT if the valves are leaking or cold water at higher pressure is back-feeding into the hot causing a PRV to operate the same dripping at the tundish will happen.

I believe that some makes of HW cylinders have a pressure gauge on the inlet set (mine hasn't) or elsewhere on the HW side. e.g. on an external pressure vessel install (mine in my last home didn't, though).  I don't know how practical they are to be retrofitted and if they give any long term issues?

Also have a look at other forums (DIY / Plumbing) for your issue in case someone who is a tradesman rather than amateur like me has any firmer ideas.

Thank you, that's really helpful. I have read so many forums without the exact same issue but many like yourself has suggested backfilling due to high water pressure and to fit a PRV to the incoming cold for similar issues. 

I found out that megaflow will under warranty fix an issue with the internal air gap for the tanks entire life, so I am going to get my dad to install a PRV and to check both the taps in the kitchen and bathroom over Christmas and then see if the issue resolves. If not, I should be able to then go back to megaflow and get them out to install the external expansion vessel. 

housebuyer143

I have tested my water pressure today and it's running at 7.5 bar, so on mentioning to Baxi technical support they now recommend reducing the pressure down and then monitoring it as they said that potentially the high water pressure could be forcing through the PRV on the tank as it's not designed to hold back that much pressure. 

He said if this is the problem then an expansion vessel will do the same thing as the internal baffle and I just have another thing to maintain. 

So we will see how it goes. PRV on incoming mains and then keep an eye on the air gap. Apparently the water coming out the megaflow is about 3 bar, so that's a huge imbalance.

 It's probably a good thing to do because my kitchen mixer is only rated to work with 5 bar. 

ListysDad

As a G3 engineer, this discussion frightens me. If your incoming pressure is 7.5B (how & when did you measure it?) it needs a PRV on the incomer to drop it to a pressure more than 3 bar but under that at which colds taps are rated. That then allows the control set on the UVC to do its job properly and you can then use the cold take off on the control set to run to showers so they are a balanced supply. 

DIY messing with this stuff is potentially pretty dangerous and can cause cross contamination of the house water supplies. I've seen blue water (from the WC cistern) coming out of a kitchen hot tap due to DIY. Additionally, once fitted, the incomer PRV should also be part of the UVCs annual maintenance.