Sealed System Pressure Leak Problem--Help!

[taxirankas]

I am new to this forum and have completely run out of ideas.
My system had a problem with sludge so I organised for a power flush and sealed system to be put in last year to stop the air corroding the system. I then found that the pressure was leaking and the water needed to be refilled from the filling loop, otherwise the boiler would fail. PRV was replaced and is not leaking at all. I have pulled up every floor or isolated every radiator but found no evidence of a leak. After isolation the leak seems to be on upstairs circuit, which also includes the boiler.
Pressure checked the vessel and this seemed fine. Put in double dose of leak sealer but to no avail. Hot water not discoloured, so does not seem to be heating coil perforation. Also did pressure test with air to 2 bar and did not find leak. The strangest thing is that the leak is not consistent. I had several weeks in warmer months when heating first put back on and no leak at all. Seems to be worst in cold weather. At the moment it is dropping one bar per day. Seems like a lot of water. The condenser boiler creates a lot of steam (Alpha CD24R). Had boiler serviced and was told not leaking (but plumber didn't seem to take it apart much). Four different plumbers have told me it very unlikely to be the boiler but I think it has to be. I was also told I can't isolate the boiler itself. Any ideas for next steps? As the leak is inconsistent I don't want to call out the leak specialists, pay 800 quid, only for them to find there is no leak/pressure loss that day.
Cheers in advance.

 

[michael c]

why cant you isolate the boiler? If this is is worse in winter i would expect it to be pipework due to expansion and contraction.

 

[taxirankas]

why cant you isolate the boiler? If this is is worse in winter i would expect it to be pipework due to expansion and contraction.

Thanks for your help. WhatI don't understand is if most or all of the loss is on the upstairs circuit (which it seems to be based on the isolation), then why would I not see this coming through the ceiling, damp patch or discolouration etc. Seems to be a lot of water loss each time I refill.
Cheers

 

[secret squirrel]

The water may be spraying gently on to a joist and may take months to show, you don't need to loose gallons of water to have the boiler on 0

 

[michael c]

1 bar of pressure is a very small amount, and if lost when hot some could evapourate if leaking onto a hot pipe. i take it there is no sign of a leak on the boiler itself?

 

[suburbanplumber]

What he said

I had something similar - it turned out to be a tiny seep from the bleed valve which was missed on several searches as the water evaporated as soon as it hit the hot radiator. You only have to lose a tiny amount of water (egg cup) to lose pressure.

One way to know for sure would be to put food dye in the system and look for the coloured stain. Another and potentially less dramatic way would be to drain the system connect your compressor to it take it up to say 4BAR and then use a stethoscope and some powdered chalk.

Let us know how you get on
SP

 

[henly1234]

I have had experiences whereby the packing gland on the valves was passing but evaporating before it became apparent.
If it seems to be the boiler then it could be a pressure vessel problem, put a balloon over the prv outlet to see if the prv is passing make, how much pressure is there it should only be enough to ensure the boiler senses that there is pressure (1bar) the prv lifts at 3.5 bar and discharges.