Hello Having exhausted all the forums on this issue I am still unsure what is causing my combi boiler to lose pressure. I have had to keep topping it up every day now for the past month, I've checked the expansion vessel and all seems to be in order (topped it up a bit with a foot pump to 1 bar). I have isolated the system for 12 hours with pressure at 1.3 bar. There was no change in internal boiler pressure after this period and upon turning the return and flow valves, the pressure suddenly dropped down to 0.6 bar. I know the other main cause of pressure loss is a leak, however to be losing over half a bar on a daily basis for a month, surely this would be noticeable by now. I also live in a 4 year old block of flats so would be surprised if any wear and tear has happened to the pipes in this time. There is what's been labelled as a 'By-Pass Valve' immediately outside the boiler, could this be the culprit perhaps? Would love to get a professional in but won't be able to afford to do so until the new year. Really want to get this resolved before then as topping the boiler up daily surely can't be good for the system? Will I need to add some inhibitor if this goes on for much longer? Appreciate any help anyone has to offer, thank you in advance!
Hi Alex. The exp vessel should really be topped up when the water side has first been depressurised, because the system pressure (the water side) can give a false reading on the 'air' side. Having said that, from what you say it does sound as tho' your issue is on the radiator side. If you topped up the system to 1.3bar and then closed the two isolators on the boiler - the flow and return - and there was no pressure loss, that does seem to suggest pretty conclusively that the boiler itself is ok. Yes, there can be some unusual circumstances where the boiler leaks only when it heats up - a joint must creak open or summat - but that is very rare; a leak is a leak is a leak. And what they do is 'leak'. So, I fear it must be on the radiator side - a rad or the pipes or summat. Not really sure what to suggest - unless you can access the pipes, then it's a sod to locate. Perhaps shove in a dose of sealer and see if it works?
The by-pass valve connects the flow and return and ensures that there is always a flow betwixt them. I can't see how that can cause a pressure loss, as it effectively joins two sides of the very same system. What does the pressure gauge do as the boiler fires up and gets to max temp? Does it go up at all?
Hi Devil's Advocate, Firstly thank you for such a quick and detailed response. I may have skipped out depressurising the system when recharging the exp vessel which might not have been the best idea in good old hindsight. On firing it up just now, starting at 1 bar it rose steadily to 2 bar within a space of 5 minutes and stopped there upon reaching temperature. I believe that's slightly more than it should although if the exp vessel was the issue wouldn't you expect it to shoot up more than it did? If it is a leak then that will be a massive task to find, so really hoping it isn't! What type of sealer would you use? I have not come across this method previously on my forum trawling, would I just go ahead and open a radiator valve and put some in? And thanks for clarifying about the by pass valve, forget I said anything on that!
If the pressure gauge previously went up to 3 bar (the 'red line') and now only goes as high as 2 bar, then that looks as tho' you've likely sorted the exp vessel issue by giving it a few pumps. Ideally I wouldn't like to see the pressure increase that much, but in practice it's well within normal, so not to worry. It's still worth checking the safety discharge pipe as mentioned earlier, tho' - this is a 15mm copper pipe which will come out through your wall nearish your boiler and point down towards the ground. Tape a clear plastic bag over that (loosely) and see if it catches any water. As for sealant, surf 'central heating leak sealer' or similar.
I've located the 15mm pipe and although it disappears and goes down into the flat below there is the release valve connected to this actually inside the boiler cover. I've put a plastic bag around this and will wait to see if I get any drops. Let's say there's none when I go to check later (after the heating has been on and cooled down), would it still be possible for the valve to be faulty without there being any drops? Thank you
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