We have a combi boiler which is losing pressure. If I top it up to 1.5 bar, within 7 to 10 days it drops to 0.75 bar. The prv is not letting by as that has recently been changed, along with the aav aswell. It has also had a new heat exchanger. The pressure drops even if the boiler is only set to hot water. The hot water works fine, as does the central heating. Before I look at pipework under the floor(ones I can get to), is there anything that might be the cause? I have heard from a colleague that if you turn the central heating taps to and from the boiler off and turn the dial to dhw only, and then leave it for as long as possible, that when you turn it back on even if the pressure drops only a little bit then there is a leak in the central heating system. Would that also apply if the pressure is going down with boiler set only to dhw? Any help would be great.
Boiler losing pressure
- Thread starter MBK73
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- boiler fault
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The pressure readout is the pressure in the central heating loop. There is no direct connection between the hot water and the central heating loop other than a thermal one via the heat exchanger and the filling loop. If you turn off the in and out central heating connections all this will do is tell you if the water leak is inside the boiler or external. If it is inside then you would normally see the water leak anyway.
Thank you. That would explain why the pressure is going down even when it is switched to dhw only. How long would I have to leave it off to see if pressure drops when I turn it back on? Would a pressure drop like that be easy to find, or is it the proverbial 'needle in a haystack'?
It is not a particularly fast leak so wouldn't be that easy to spot. If a plumber takes a look at your house they might have some ideas where it might be leaking. Anywhere upstairs you are probably going to see damp spots on the downstairs ceiling etc...
In my house I got a plumber in to install a gate valve in the 22mm pipe as ot comes off to go to the downstairs radiators. I then made my own section of pipe dropping 22mm down to 3 microbore 10mm pipes with isolators. I them turned each off in turn to find what section of pipe was leaking.
It got quite bad by that point as it needed topping up twice a day and I found I had 'trace & access' on my home insurance so they got someone out to find out where along the pipe it had leaked. The pipe was buried in the concrete floor and went up and over the gas pipe. There wasn't enough room to cater for heat expansion so the pipe kinked and eventually it just broke. Everything was covered apart from the pipe repair itself which I didn't pay for either as when they were digging up the floor they managed to put a perfect central hole into the gas pipe so fixed the regular pipework when they were fixing the gas pipe!
In my house I got a plumber in to install a gate valve in the 22mm pipe as ot comes off to go to the downstairs radiators. I then made my own section of pipe dropping 22mm down to 3 microbore 10mm pipes with isolators. I them turned each off in turn to find what section of pipe was leaking.
It got quite bad by that point as it needed topping up twice a day and I found I had 'trace & access' on my home insurance so they got someone out to find out where along the pipe it had leaked. The pipe was buried in the concrete floor and went up and over the gas pipe. There wasn't enough room to cater for heat expansion so the pipe kinked and eventually it just broke. Everything was covered apart from the pipe repair itself which I didn't pay for either as when they were digging up the floor they managed to put a perfect central hole into the gas pipe so fixed the regular pipework when they were fixing the gas pipe!
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If your heating is switched on, small leaks will evaporate as quickly as they leak. However the taps test would be a good one as if the hex has been replaced the could be a leak at the joint our a fault, causing the leak to go down the condensate drain.
Is it possible to see if it produces condensate even when it's off?
Are you sure your aav was replaced? If so that's not really related to the heating primary loop.
Is it possible to see if it produces condensate even when it's off?
Are you sure your aav was replaced? If so that's not really related to the heating primary loop.
Tie blue paper tissue around all of your rad feed pipes (just below the valves) and check with heating off and heating on - sometimes a leak from compression joints occurs only when ‘hot’ or only when ‘cold’. Also a leak can occur as said, within the hex and water run away down the condense drain. Can you easily get to the end of this and direct it into a plastic bag tied round it? The boiler would have to be left powered “OFF’ for a considerable length of time.
Other than that it might be out of sight and from old pipework under pressure.
Other than that it might be out of sight and from old pipework under pressure.
You can start by creating your own thread rather than hijacking the Op's.
Then you can go to the gas safe register website and look for a professional in your area as you shouldn't be poking around in there.
Just a quick update - Had British Gas around, and they seem to think it is the Main Heat Exchanger leaking causing the pressure drop. He ordered the part and came today to fit it, only to realise it was the wrong part! He then went on to say that the parts dept may not be able to get correct part as it could be obsolete. He said that the leak has caused the parts inside to go rusty, so no good - he arranged for a heating specialist to come and give us a quote for new boiler next week(someone phoned later to offer £700 off). After he went we phoned boiler manufacturer who said part is not obsolete, and provided local suppliers. Both can get part to us in 24 hours - so why can't British Gas? He must be on commission for sales!! When BG phoned later to offer the discount, my wife told him we could get the part, he was surprised and said that they would hopefully get the part. BTW, boiler works fine(ch and dhw), apart from pressure drop.
British Gas is not British! A private company bought the name and trades on the heritage... don’t be taken in like the 1000’s that are.
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