Megaflo expansion tank pressure drop

[Cambs1]

Hi all,

Thought I'd see if we could solve our Megaflo problem with this site. It looks like people have had some sound advice!

Our house is about 4 years old and has a Megaflo installed on the ground floor and the Vaillant boiler is in the attic. It has given us no problems until the last few weeks. The gauge on the red expansion tank above the megaflo tank shows a pressure drop over 48h and then the boiler stops due to the low pressure. I need to top of the red tank and then reset the boiler. All is well until I need to do this again in 48h. I'm not sure whether the drop is gradual or sudden, but seems to occur overnight. The pressure never drops to zero. Could this be a problem with the cold water feed - a blocked filter??

Any advice would be much appreciated.

Happy New Year by the way

 

[Phill Peck]

Megaflo cylinders have internal expansion vessel
Normally this red tank would be for your boiler but Vaillant system boilers also have an internal expansion vessel unless your boiler is a 4 series

The problem will most likely be either a leak or this red vessel has failed

Have you seen any signs of leaks or dropping discharge pipe outside

 

[oilman]

To check expansion vessels you need to reduce the system pressure as you pump air into the expansion vessel. When the air pressure is about 1 bar, you can recharge the system to 1 bar. I suspect the expansion vessel has not been checked since installation.

 

[Cambs1]

Thanks for your reply.

Since I topped up the red tank to 1.8 bar and reset the boiler 5 hours ago there has been no pressure drop - in fact it's gone up to 2 bar and has hovered just below there ever since (with hot water and CH on). No sign of a leak so far, but we do have underfloor heating downstairs run off the CH system.

For the first time, I have seen drips coming down through the tundish - we have never recharged the air gap - would this solve the pressure problem in the red expansion tank??

Many thanks..

 

[Agile]

They are completely seperate systems.

Reform the air bubble as described on the outside.

If its now working then I would say dont touch the boiler although the pressure is too high. 1.5 Bar cold is ideal. Bleed water out of the rads.

If it gives problems then refill orange with air as described in the FAQ but ignore the 10 litre bit ( why can't I or someone edit it?

Tony

 

[Cambs1]

Cheers Tony - so the small red tank above the megaflo is actually not for the megaflo but for the boiler? Upstairs CH is radiators and downstairs is piped hot water underfloor (we would never choose underfloor heating!! - takes 2 years to respond to any alteration in temp!)

Could a pressure drop be due to a boiler fault causing water to exit the boiler through some sort of overflow pipe into the guttering? Boiler is in attic so I have not located any sort of overflow pipe. Definitely not found leak upstairs.....so far

Sorry I seem to be yo yo-ing all over the place, but I'm trying to get my head round what seems to be a complicated system.

Ta

 

[Cambs1]

Well guess what - I have found a LEAK! A bit quicker than the poor chap that realised someone had banged a bookcase nail through one of his hot water pipes! One of the valves to one of the underfloor heating pipes is dripping slowly on to the concrete screed. At least it's accessible.

Thanks for all the help. I great site!

Cheers and Happy 2012!

 

[Agile]

Cheers Tony - so the small red tank above the megaflo is actually not for the megaflo but for the boiler? Upstairs CH is radiators and downstairs is piped hot water underfloor (we would never choose underfloor heating!! - takes 2 years to respond to any alteration in temp!)

Ta

I am interested to hear that assessment. Its what I always like to warn people about.

But I am up against installers whose prime interest is getting jobs to do rather than fitting whats best for their customers.

UFH is fine in libraries and old people homes and for retired people at home all day as well as mothers at home with young children.

But it does not suit people with irregular hours. Or for those like me who like a cool bedroom.

Tony

 

[Phill Peck]

Cheers Tony - so the small red tank above the megaflo is actually not for the megaflo but for the boiler?

Ta

"cheers tony"
Did you not read my post

 

[Cambs1]

Yes! Thanks to you gasservice 1985 - you said a leak or the vessel itself and you were spot on. Judging by what's accumulated in a bucket overnight, I dread to think what volumes leaked into the screed over the last week or 2. The wooden floor's not lifting yet though!!