Megaflow problem for last 15 years - tried every expert.

Paul989

I have an oil heating system with a megaflow water system professionally installed 15 years ago.  Works PERFECTLY.... except for one very strange issue.
I know that the megaflows need occasional "regapping" to re generate the air gap, however mine needs regapping EVERY 2 MONTHS.  - without fail, summer, winter, if the system is used a lot or very little (away during holidays) - its ALWAYS EXACTLY every 2 months.   I thought this was normal but lots of other megaflow users re gap sometimes every couple of years.  I did try the megaflow help lines but no one seems to know. 
Any ideas?

akira181

You've not said what model of Megaflo you have but I think they all have an internal expansion vessel / diaphragm. 

It's a disc the width of the internal cylinder which separates air (above) from water (below). When the water is heated, it expands, and the diaphragm is forced upwards, compressing the air above it and maintaining a constant water pressure in the cylinder.  The air escapes over time and needs to be recharged, usually annually.  If the diaphragm is stuck, dislodged or punctured, it'll lose air faster and require more regular top ups.  The seal is also affected if there is limescale build-up on the internal walls.

Considering the age of your system and I'm assuming this frequent recharge is a recent development, I suspect this is the case.  If so, the cheapest option would probably be to get an external expansion vessel professionally fitted.

Alternatively, it could be that you are not fully recharging the air gap when you do it.  The cylinder needs to be sufficiently drained to allow enough air in to fully recharge the expansion side.  I don't know if your model has different instructions, but just running the lowest hot water tap for a few minutes is not enough to drain the cylinder sufficiently, as the hot water draw off is from the top of the cylinder.  More often than not, you need to drain some water directly from the base of the cylinder as well to allow enough air in to fully recharge the gap.  I would try this first if you haven't already, the instruction manual should tell you how.

Jeepers_Creepers

Hi Paul.

Never heard of 'regapping' - this forum is an education :-)

Do you do this job yourself? When you press the Schrader valve (I'm guessing that's what it has?), does any water come out? Does it go completely 'flat' every two months - no air at all? And, when you repressurise it, how many 'pumps' does it take, and using what device?

Akira's point is a good one - to check it's being done properly. This also applies to combi and system boilers with built-in EVs. If you imagine the cylinder/vessel which has a rubber diaphragm in it, one side has the system water and t'other has compressed air. If the air escapes, the water side will fill the vacated space. Now, when you come to recharge the air side, you are pumping in to a reduced space which has a wall of uncompressible water on the other side - ergo, a few air pumps and the pressure is seemingly restored. However, the air volume is tiny and won't serve much purpose.

So, the correct way is to fully release the pressure from the water side first (open rad bleed screw and release system pressure on combi and leave screw open during charging, and (I presume) shut off cold inlet supply and open hot tap if a megaflow), so that when you recharge the air side, the diaphragm can expand properly to the volume and pressure it should be at. It'll push more system/hot water out the bleed screw/tap as you do this. Then close bleed screw/shut off tap, and repressurise boiler/ open cold inlet. 

Browntoa

That's an extremely short period to have to keep doing this to a megaflo.

I take it you are doing the proper turn off cold water feed , fully drain hot water , refill with water while adjusting the grey knob until it stops dripping water ? 

robatwork

This isn't an answer to your query, but I have a Megaflo, and the performance required to regenerate the air gap does to me fall outside what I'd expect a consumer to have to do with domestic equipment maintenance. I posted this thread recently https://forums.moneysavingexpert.com/discussion/6217801/megaflo-is-a-design-flaw-built-in#latest 
but not much response from plumbers. Plenty of forum postings elsewhere about how this is a design fault - perhaps you'll be the one to take them to court - every 2 months is crazy!

fezster

Every few months is not uncommon. Its a poor design and I ended up having an external EV fitted, as I got so fed up with it. Would never buy an overpriced megaflo again. 

Paul989

So yes its a CL210 model, with the external red expansion cylinder.  I have to do it every two months because the overflow from the unit starts dripping a lot and the amount of hot water diminishes.  I follow the instructions on the side of the unit to the letter.  Turn off the mains to the system, open lowest hot tap, open the valve on the side and wait for the water gurgling to stop.  Strange that its happens since nearly new (15 years) and always 2 months.