Sealed System Install - Take 2

[cr0ft]

Hi all.

Myself and a gasfitter on these forums are off to look at a combi-boiler install tomorrow that I did last Christmas. All central heating pipework was pressure tested prior to fitting the boiler and passed a pressure test at 5 bars.

Since the boiler has been installed the pressure is dropping every day, usually by around 0.3 - 0.5 bars. I've checked everything I can think of and I'm still at a loss, especially as there are no signs of a leak and this sort of pressure drop equates to a loss of around 1 litre a day. This would certainly be noticeable.

FACTS SO FAR: -

The leak occurs whether or not the CH is on, we've left the heating off for a day and it still does it.
The PRV isn't leaking at all.
The expansion chamber is working fine, pressure rise on heating up is around 0.2-0.3 bar, pretty normal.
There are no signs of leaking from inside the boiler.
The pressure gauge definitely isn't faulty as the boiler is cutting out when it drops to 0.4 bar (the low pressure switch for this boiler - a Broag Avant Plus 39C combi). This is how we first found the problem.
I have been over all pipework in the house with an infrared camera. There are no signs of anything unusual, i.e. no black patches indicating damp.
All radiators downstairs are fed by microbore pipework inside dot and dabbed walls. There are no CH pipes running under the ground floor.
2 inaccessible dead legs (the old feed and expansion tank pipes) have been capped off with automatic air vents in the loft. Thermal imaging shows both of these pipes are full of water.
All radiators are full of water.

I'm at a complete loss, does anyone else have any ideas? If we can't sort it tomorrow we are looking at re-plumbing the whole system to stop the problem. Definitely not a cheap option for my customer.

 

[villa_tom]

Are you sure the customer is not messing with it, ie venting rads etc? Sounds like you have done all the tests you can and have shown up with no leaks.

When I was doing my apprenticeship the bloke who trained me told me a story about a friend of his who did an install in a property for an old lady who had never had central heating before jst 2 gas fires. Everyday the elderly lady would wake up and the boiler had gone to lockout, he tried evrything and went back day after day but could not find anything. Eventually he replaced the boiler free of charge. He went round the next day to check if it was okay and when he turned up the old lady went straight to the gas meter and turned it back on. It turns out every night when she went to bed she would turn the gas meter off at the ECV.

 

[steosman]

Pressure test the coil on the hot water storage cylinder, possible a faulty coil, very unlikely but worth a shot.

 

[stani]

have you tried blanking off the auto air vents then letting it work over night, I have recently had a problem where an AAV was dragging air into the system as soon as it started up,

 

[doitmyself]

Can you isolate the boiler and then do a pressure test on the system pipework? This would tell you if the pressure drop is in the boiler or the pipework. If it's the boiler, then go back to Broag; if it's the pipework you can do further investigations.

See page 2 of the topic "any ideas???"

 

[stani]

am I right in thinking its a combi?

 

[steosman]

sorry didn't see it was a combi

 

[stevetheplumber]

if its possible your going to have to section the system to locate leaks
ie valve off up and down circuits and hw
i would definately remove aavs and swop for manuals ,aavs are always a pain inside and outside of boilers

 

[Billy Bob Bob]

i agree with Steve section the pipe work,be dubious of any pipe work in cement floors,its unlikely but rule out the main heat exchangers not failed and losing water via the condensate pipe

 

[stani]

i agree with Steve section the pipe work,be dubious of any pipe work in cement floors,its unlikely but rule out the main heat exchangers not failed and losing water via the condensate pipe

doesnt it say there are no pipes in the floor?

 

[Billy Bob Bob]

doesnt it say there are no pipes in the floor?

lol did it say it was a combi?

 

[stani]

if I wos quiker typing that wood have gone at numbr 4 and made sense.........

 

[Billy Bob Bob]

if I wos quiker typing that wood have gone at numbr 4 and made sense.........

i am teasing you,just watch those green houses lol

 

[stani]

reckoned you was!!lol

 

[stani]

at this rate I should get my 100 postings tonight.

 

[Billy Bob Bob]

at this rate I should get my 100 postings tonight.

go for it you can join the arms then if you want to

 

[stani]

No no, i'm an employee

 

[Billy Bob Bob]

if your a plumber you can join the arms you dont need to be gs or working for a large firm or prove your qualifications just have a hundred + posts so technically 101 and your in

 

[stani]

sorry, I was under the impression that Plumbers arms was for sole traders/businesses, perhaps a note on the site to explain how the relevant==junior/member/senior/plumbersarms system works, unless of course its already there and i have'nt seen it. lol

 

[Billy Bob Bob]

sorry, I was under the impression that Plumbers arms was for sole traders/businesses, perhaps a note on the site to explain how the relevant==junior/member/senior/plumbersarms system works, unless of course its already there and i have'nt seen it. lol

no just professorial plumbers with 100+ posts,its on the forum header on the arms,as your posts increase your status goes up,junior member (i think?) member,senior member,if you join plumbers arms member

 

[diamondgas]

Pressure loss is a water leak! You have one somewhere my friend! If the expansion vessel is fully charged and nothing is visible you could try leak sealer. Injected into the system it solidifies on contact with air and , supposedly, seals the leak! Only other possible issue could be a wild card blockage to the expansion vessel! mho!

 

[tamz]

Check the boiler as gasman says. It could be getting through the condensate pipe.
Pressurise it and isolate the boiler for a while. If the pressure remains steady or drops then you know for definite if the leak is from the boiler or system.

 

[cr0ft]

Thanks for all the feedback so far. Heat exchanger leaking through the condensate pipe isn't something I'd considered. As the leak equates to 1 litre a day or so it would be noticeable by now if it was inside the building. The IR camera would have picked something up too.

Will isolate the boiler and check it separately tomorrow. Going to be a fun day. I don't think the AAVs would cause system pressure to continuously drop - the system would need to be losing so much air it's silly to cause the pressure drops I'm seeing. If it's sucking air in the pressure would increase surely?

Thanks to all for help so far, I'm truly stuck tbh.

 

[Billy Bob Bob]

a failed heat exchanger would cause this kind of drop as would a big leak is there a clear trap on this boiler?

 

[tamz]

I'm truly stuck tbh.

If it is on the system somewhere there is always this
Leak Sealer | Liquids | Central Heating | Sentinel central heating products
It works.