Megaflo Air Gap Problem

[JimG63]

I have an ongoing problem with my 10 year old Megaflow tank. After approx 6 weeks the air-gap gets reduced to the point where water comes out of the T&P valve when the system heats up. The air-gap has been re-set several times and the result is the same. The T&P valve was replaced on the advice of Heatrae but water now comes out of the “expansion” valve instead. I suspect a very slow leak in the tank but it’s very difficult to be sure as it’s encased in foam. I live in a close of 9 houses all with the same system and I’m the only one with this problem which should rule out environmental factors.

Does anyone have any ideas before I fork out for a new cylinder?

JimG

 

[Agile]

Fit an external white 12 litre expansion vessel !

Set it to the same air pressure as the working pressure of the cylinder before pressurising the cylinder.!

Toiny

 

[JimG63]

Thanks Toiny,
I had wondered about this but was a bit uncertain. Is 12L enough - the tank is 210L?
JimG

 

[simond]

If you have a small air leak from the cylinder the expansion vessel fix will be shortlived. Someone will have wet feet soon.

Is the standing pressure before the combi valve very high? If it is near 6 bar static then the valves will let by once the combi valve gets grit or corrosion in it.

 

[DP]

Why not talk to Megaflow people. Cylinder carries a 25 year warranty

 

[simond]

If its a 1998 model it'll be made by Davtec and may not have the long warranty......

 

[JimG63]

Thanks for your comments. The warranty has long since expired - it's only the new ones have 25 years. Despite the problem going on for some time (the leak would dry up overnight so it wasn't obvious that there was a problem!) there is no evidence of water leaking from the tank itself. The pressure on the input side is OK (according to my plumber) and the water leaking out of the combi valve is slightly warm so it would seem to be coming from the tank rather than the supply.

 

[Agile]

Thanks for your comments. The warranty has long since expired - it's only the new ones have 25 years. Despite the problem going on for some time (the leak would dry up overnight so it wasn't obvious that there was a problem!) there is no evidence of water leaking from the tank itself. The pressure on the input side is OK (according to my plumber) and the water leaking out of the combi valve is slightly warm so it would seem to be coming from the tank rather than the supply.

What that implies is that the leak is from the T&P valve rather than the 6 Bar PRV at the inlet.

However disconnecting some pipework would confirm that.

I dont expect there is any leak in yuor cylinder.

More likely that local conditions or your pipework is prone to the air bubble getting dissolved.

Does your "plumber" really have the qualification for unvented cylinders?

If he cannot diagnose simple faults then his credibility is very questionable!

Tony

 

[JimG63]

Thanks Tony. I disconnected the pipework to the tundish and I can see that the leak is definitely from the expansion valve rather than the T&P (original leak was from T&P valve and this was changed anyway on advice from Heatrae). In my opinion the valves are opening as they should due to the high pressure in the tank which in turn is due to the reduced air gap (evident when you reset the gap). No one else in our close has the problem and we all have identical Megaflows - is it possible that the air gap could disappear in 6 weeks due to "natural causes"? I really don't know what else I can check?

 

[Agile]

Its sounds unlikely but 6 months is normal, a few do 3 months and some never seem to need recharging.

Possibly the moving baffle is jammed and not covering the water/air interface.

Since an external EXV will cost about £100 installed then its less that a tenth of a new cylinder that seems th way to go! If you can fit it yourself then its only about £30 to buy!

Tony