Mystery of Pressure Loss

[venton]

Had open vented system replaced with Combi boiler 3 months ago. Firebird Enviromax Oil condensing boiler.
Had pressure dropping for last 6 weeks, needs topping up with water twice a day. Pressure dropping from 1.5 to 1.
Here's the clues - any ideas?
No sign of leak internally to house. Just had detector guy round with thermal camera and listening device. Not a sign. He doesn't think there is a leak.
I put a glass under the condensation pipe for 48 hrs. Got about half a wine glass. The water looks a bit pink, like Rose. Didn't taste it!
Got balloon over relief pipe, nothing coming out.
I just drained the system and boiler. As it happens the gauge is reading wrong. Empty is showing as 0.5 on the gauge. So actually system has been running at between 1 bar and dropping to 0.5 bar.
With everything drained, got both pressure vessels up to 1 bar.
It was drained to get rid of some Fernox f4 which had been put in and did nothing.
So, clues are:
Pressure dropping
No sign of leak
No leak from PRV
No leak around boiler.
No obvious leak from condensate pipe, but there is some liquid collecting here (it's meant to collect some isn't it?).
Any ideas? Ta.

 

[johnf]

Nothing jumping out at me! Have you got quite a few dead legs on the system? The air pockets could be finding their way out of the system through AAV's.
Something is coming out somewhere be it air or water. If your man with the listening stick and thermal camera says no leak of water then it has to be air.
The condensate pipe is meant to discharge water which is formed as part of normal operation of the boiler

 

[venton]

Only 1 short dead leg I'm aware of.
Is it possible for water to escape out during combustion due to a weird fault?
It's quite maddening as water is being put in each day, but can't be detected coming out.
The detector guy will come back with gas testing kit, even though he's reluctant as he sure there's no leak.
On the other hand, the boiler installer is insistent it can't be the boiler.
I'm stuck in the middle having a nervous breakdown!

 

[johnf]

If water was escaping you would see it. If it is under a screed floor the thermal image camera should pick it up.
Is he coming back with tracer gas? If so this will trace a leak if there is one.
Good luck

 

[venton]

Thanks John.
Yes he is prepared to come back, but it's two hours each way for him, so I hope it's not wasted time.

 

[Best]

Just possible there is a leak at the boiler, so don't rule it out straightaway.
Boiler shell or secondary exchanger could potentially be leaking internally and you won't know as the water will come out as steam or condense. Sometimes they leak at a crack only when boiler heats. I saw a boiler that was leaking at base, but didn't show because it only really leaked when boiler was hot and most water must have just evaporated.
I would have thought leak sealer would have helped though, if you had that problem.

 

[Frog67]

Have you been round and checked all the radiators and any exposed pipe work for leaks?
Look for signs of water damage/leakage on valves and air screws/plugs etc.
Very small leaks can occur when the system is hot (expansion).
Check everything when the system is cold
Another thing to try (although not ideal at this of year) would be to isolate the boiler from the central heating for the time it takes to loose its pressure.
If pressure stills drops then the problem is with the pipework
If pressure is stable then suspect problem with boiler.

 

[ShaunCorbs]

If pressure stills drops then the problem is with the pipework
If pressure is stable then suspect problem with boiler.

yes or no depends where your pressure gauge is if on boiler

no drop once valved off from heating system means boilers ok
drop once valved off from heating system means leak inside boiler

 

[venton]

I've isolated the boiler overnight and no drop on gauge, which measures boiler pressure.
My concern is that the pressure drops during firing, not sure if that is possible.
It seems to drop more pressure the colder it is, ie boiler running more.

 

[ShaunCorbs]

I've isolated the boiler overnight and no drop on gauge, which measures boiler pressure.
My concern is that the pressure drops during firing, not sure if that is possible.
It seems to drop more pressure the colder it is, ie boiler running more.

well if theres a leak on the boiler will show in the morning dont forget DONT TURN YOUR HEATING OR HOT WATER ON

 

[venton]

Just possible there is a leak at the boiler, so don't rule it out straightaway.
Boiler shell or secondary exchanger could potentially be leaking internally and you won't know as the water will come out as steam or condense. Sometimes they leak at a crack only when boiler heats. I saw a boiler that was leaking at base, but didn't show because it only really leaked when boiler was hot and most water must have just evaporated.
I would have thought leak sealer would have helped though, if you had that problem.

Leak sealer did slow it down for a few days, but had no idea where the leak was of course.

 

[Best]

Leak sealer did slow it down for a few days, but had no idea where the leak was of course.

Maybe a service engineer looking inside the boiler might be fruitful. I was asked about a leak in a combi oil system and after first blaming the expansion vessel lack of air charge, it was later found to be inside the main boiler shell. Luckily the 4 year old boiler had 5 year warranty