Megaflow Tank Losing Pressure

27 Nov 2010
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United Kingdom
Hi Folks could anyone help me with comments/info about Megaflow Tank Pressure loss?

Over recent months I've noticed a steady but slow pressure loss from my pressurised cetnral heating system (Worcester boiler, Megaflow tank model CL250) I've topped up the pressure, but last night there was a very quick loss of pressure (red expansion tank pressure dropped from 1.5 to zero literally in minutes). I have re-established the air pocket in the Megaflow, same again, pressure falls quicky to zero (accompanied by a hissing sound which "seems" to sound internal to the Megaflow tank)....internal failure in the tank coils? Anyone any experience of such a failure or any other comments? Cheers.
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I have re-established the air pocket in the Megaflow, same again, pressure falls quicky to zero

I can follow the pressure dropping in the red expansion vessel but not sure what you mean by the above quote, if the megaflo coil was leaking into the hot water you would probably have noticed the dirty/inhibited system water coming out of the taps,re-establishing the air pocket wouldent have any effect on the system pressure, any chance of a picture ?
Thanks Picasso, a picture's not possible at the moment.

The central heating system was pressurised & the pressure was falling. I thought that the airpocket in the Megalflow tank might have been a possible issue because when the boiler was on water was dripping quite a lot into the tundish (suggesting that the air pocket needed I did that). Meanwhile the pressure in the system had fallen to zero. I brought the pressure back up to 2 to 1.5 & as soon as I'd closed the water valve to the red small expansion tank pressure in the system started to fall again & quicmly (minutes) fell to zero...while doing so there's a audible hissing sound (as clearly the pressure is losing out of somewhere). There is no dirty water coming out of the hot tap, the whole C/H system was put in just 4 years ago. My question is could there be a leak in the internal coils of the Megaflow which is causing more water to go into the tank which then leads to the water dripping/flowing into the tundish when the heating is on. The pressure showing on the gauge on the red small expansion tank is zero & unless I open the water supply to that tank I can't get the pressure in the system & can't run the C/H system unless that valve is slightly open so allowing water into the system & keeping the pressure up (if that water in valve is closed the pressure immediatley falls)
close the cold supply to the cylinder , open a hot water tap and then open the supply to fill the radiators, if you get water from the tap you will know the coil is split. you will get some hot water at first when you open the tap , this is the pressure of the air gap pushing the water out let this stop then open the filling loop.
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Thanks again Picasso, I'm struggling to work out how to do what you've described, I better get someone in to look at it. I've just pressurised the system up again (open water valve on smalll red expansion tank, gauge rises from zero to 1.5 to 2, close that valve). Pressure then immediatley begins to drop accompianed by a low buzzing sound (like the noise you get when letting the air out of a balloon stretching/pinching the neck). This noise is coming from the area where the pipe goes into the Megaflow tank & it is labelled Primary Return. I'm at a loss other than to think there's a problem with the coils inside :confused:
Have a look outside and see if water is coming out of the prv when you fill the system, should be easy to see with the amount of water your putting into the system.
Ok, next step in the story Picasso. Can't see anything outside ...because of the 10inches of snow we have here :eek:

So....disconnected the condesntate from the boiler to the outside drain line & hung it into a 2 gallon bucket...pressurised the system (as per before) up to 2 on the gauge on the red small expansion tank...boilers on, pipes heating up, radiators hot all looks fine...but pressue is dropping ..meanwhile the condensate is spewing out & fills the 2 gallon bucket in about 10mins... Turn heating off (by this time pressure has dropped to zero) and condensate flow eventually stopped. Try pressuring system again (up to about 1.5) with boiler switch off... & condensate starts running's hot & it's yellowish...

How terminal does all this sound? Clearly all that water I've been putting in is ending up coming straight out of the boilers condensate line...
need to clarify what you call a condensate line, is the pipe all copper going to outside or is it a plastic pipe connected to a drain ?
The plastic pipe I disconnected is the one that is connected between the boiler & a plastic pipe which then runs to the outside, under the house tiles & into the gutter of the house (that's the boiler condensate line as I know it). It's a plastic pipe, not copper.

During the heating being on there was no water dripping into the tundish...everything was looking/sounding normal except that the pressure in the system was dropping all the time & the boiler condensate line (disconnected from the usual connection between the boiler & that plastic pipe running outside) was spewing water (running like a tap flows) into the bucket, in fact the bucket overflowed in the end.
Then the heat exchanger is holed, seems strange in a system only 4 years old
Indeed & just 4years heat exchanger I take it you mean the heat exchanger in the boiler? The boiler is Worcester Greenstar 40 cdi Conventional...
yep heat ex in the boiler, it might be worth checking what warranty you got with the boiler, they were doing a longer warranty on the heat exchangers, although it might be somewhat different in the real world getting them to honout it.
Thanks for your help & comments Picasso...the boiler it replaced had lasted 20+ years & was fashioned out of granite.... clearly these days they're made out of paper :( bother in law (who's big on DIY) had said sometime back that there were supposed to be lifetime "issues" with aluminium based heat exchangers vs stainless steel ones. This boiler I have has an aluminium/silicon heat looks like I just learned about the aluminium vs stainless steel story the hard way
The pressure drops WITHOUT the heating system being switched on.

I think my overflow is not properly connected to the drain and water drips into the kitchen through the roof.

It started when I found a pool of water onm the kitchen floor above the megaflow system. Shut the boiler off.

Megflow tank very hot. Hissing sound. Followed the steps on the label to reestablish the airgap. Lot of gurgling sound. Reopened the cold water inlet. Left the boiler switched off. The leak stopped.

Next day checked the pressure by the red bottle. It was zero. Increased it to 1 Went downstairs and water was dripping again even with the boiler off.
checked the pressure again, back to 0!

So repeated the process re the airgap. more gurgling and hot water coming out. opened the cold water inlet when it stopped. No leak.

But if I increase the pressure again it will leak again.
Any thoughts on what's wrong appreciated.

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