Slow boiler pressure loss

[lockdown1234]

Hi all,

I've got a Vaillant combi boiler that's suffering from an annoying pressure loss problem.

We've obviously not got the heating on, and haven't for a while, but I am consistently losing around 0.1 bar a week. If I top it up to 1.2, then it's down to 0.8 after four weeks, and the cycle starts again.

I've been around all joints and radiators and can't find anything. There's nothing coming from the external overflow.

When I called a local engineer his response was that it would be hard to find anything that small, so just bung in leak sealant, which didn't sit right with me, and when I spoke to Vaillant they said I could pay for a boiler repair, but that it would be hard to find a leak like that in a boiler.

I've read about isolating the boiler, but don't think it's practical to go without hot water for a week.

Is there anything else I can do or do I just live with it, wait for it to get worse, or just keep trying different engineers until I find one interested in finding leaks?

Thanks!

 

[CountryFan]

Isolating the boiler means you don't have heating, but can have hot water.

 

[lockdown1234]

Isolating the boiler means you don't have heating, but can have hot water.

Oh, I think the post I saw said to turn all power off too it. Is that not necessary?

 

[CountryFan]

Oh, I think the post I saw said to turn all power off too it. Is that not necessary?

No it isn’t necessary at all.

 

[lockdown1234]

Thanks. What I'm doing at the moment is monitoring it so I can get an accurate time line of what I am losing when, as I assume it's not doing any real harm and I figured the more information to go off the better.

One thing I did notice - I bled radiators before the last top up and there was air in some. We had our system drained down last year so could this all just be caused by air still making its way out?

 

[lockdown1234]

Ok, so it took 21 days to drop from 1.2 to 0.7. By all accounts this sounds like a very small leak that I am going to struggle to find. Other than finding an engineer that's not just going to chuck leak sealant in is there anything else I can do to find the leak?

 

[Johntheo5]

Have a look at your boiler MIs and see what capacity EV its got, if its a 10L and the pressure falls from a cold filling pressure of 1.2bar to a known precharge pressure of 0.7bar then its lost well over 2L(2.27) in 21 days, not just a drop or two, would expect almost a year with those sort of numbers.

 

[lockdown1234]

Ok, using your numbers 2.27L is 0.075ml a minute, which goes back to my original question of are there any tricks to sorting something that small?

The PRV copper pipe runs over two metres before exiting the wall, so I would think the water would be evaporating before it got to the end of that

 

[jj4091]

Not a plumber/heating engineer but if you have isolated the heating side and you still loose pressure then it would suggest that it is the boiler itself. When our heat exchanger sprang a leak the water evaporated but it was discovered by staining left behind. I would have thought a heating engineer could discover that or at least rule it out.

 

[lockdown1234]

I've not done any isolation yet, as I wanted to get a handle on the loss rate.

I will get an engineer in, but like I said, the ones I've spoken to so far just wanted to chuck leak sealer in. If anyone knows someone decent in Gloucester give me a shout!

 

[Johntheo5]

Ok, using your numbers 2.27L is 0.075ml a minute, which goes back to my original question of are there any tricks to sorting something that small?

The PRV copper pipe runs over two metres before exiting the wall, so I would think the water would be evaporating before it got to the end of that

If isolating the boiler doesnt show anything it might be more prudent to just renew the EV as a first step as these can allow air to seep through the diahragm (permeable?) after years of usage.

 

[jj4091]

I've not done any isolation yet, as I wanted to get a handle on the loss rate.

I will get an engineer in, but like I said, the ones I've spoken to so far just wanted to chuck leak sealer in. If anyone knows someone decent in Gloucester give me a shout!

I've never used sealer in anything other than a car and it was a disaster. Blocked up everything apart from the leak. I would be worreid the same thing might happen in a boiler.

 

[lockdown1234]

Alright, thought I would give you all an update on this.

So as you know, I was consistently losing 0.1 bar every five to seven days. It did this for about three months.

Towards the end of May I topped it back up to 1.1 degrees. This is a digital display, and the temperature read 26.

I went away for the week, and when I came back, the pressure had dropped to 1.0, and the temp read 23 (presumably because we hadn't used hot water for a while) and so I thought the cycle was starting again.

However, when we were back to normal usage of the hot water, the pressure went back to 1.1 and stayed there, with the boiler temperature at cold reading between 27 and 31.

I was doing these readings at the end of the day before the kids baths, the hot water hasn't been used since the morning showers.

The pressure stayed at 1.1 for eleven days, so I thought it was finally sorted.

Then last Friday the boiler pressure went up to 1.2 and it's stayed that way all this week, but obviously it's been a bit warmer out and the boiler temp was reading between 31 and 34 degrees.

So I was thinking that maybe I had air in the system and it took a few months for it all to get out via the aav, and that's why I was seeing those pressure drops.

I put the increase in pressure down to the recent hot weather.

However, I've just looked now, the boiler temp is 33 and the pressure is 1.3 so it's fine up again!

Have I just got a really sensitive pressure gauge and can this recent weather allow for that, or is it likely that I've still got air knocking around in my system that's playing havoc with the readings, or something more sinister?

 

[kidgreen61]

I think you are worrying too much, if it stays at around 1 bar, then leave it alone, if you had a leak, it would soon drop to zero.

 

[foxhole]

Boiler will function down to almost zero pressure.