Pressure loss in sealed central heating system

[Willix81]

I have a sealed central heating and hot water system running off of a Alpha CDR18 boiler. It has been experiencing significant pressure loss (from ~1.0 bar down to 0.2 bar) after the heating has been on and the water cooled back to room temperature.

No water loss from the PRV (balloon put over the pipe) and the addition of 2 doses of sentinel leak sealer reduced the pressure loss for 2 days, but it has now returned. No signs of leaks in pipe work or from radiator valves.

When cold and the boiler off (with system pressure at 1.0 bar), pressure loss is negligible - 0.2 bar over 12 hours - surely it'd lose more if there was a leak in the pipe work?

Pressure loss of ~0.8 bar when boiler has been on for several hours (from 1.0 bar cold to 0.2 bar once cooled back down.

System pressure rises to 1.8 bar when boiler on and water hot. Holds this pressure for full time boiler is on and then falls to 0.2 bar when off and cooled.

Even if starting cold pressure is 0.2 bar, hot pressure still rises to 1.8 bar (according to the gauge) and the system works fine (rads piping etc).

Could this be a leak within the boiler heat exchanger (and loss of water out the condensate pipe)?

Only other options could be a leak in underfloor pipe work, or from the coil in the unvented cylinder?

Any advice appreciated. Want to rule out a boiler issue before I go looking for leaks. Anything I could try to diagnose etc.

Thanks!

 

[kris]

Struggled to read by I get the just, unfortunately you need an engineer round to fix the pressure problem unless it's a simple leaky rad but my guess is if the pipe outside is passing water from your boiler then engineer needed,
What you can do as a homeowner check that pipe outside n if dry feel all radiator valves to make sure no leak, sometimes a knock with a Hoover can cause,,
welcome to the forum Willix,

 

[kris]

When I say pipe its a small 15 mm pipe that runs from boiler to outside, think of it like an overflow, if that's wet or dripping then defo boiler

 

[Willix81]

The 15mm White condensate pipe?

if that drips when the boiler is off does it suggest a leaking hear ex?

 

[Willix81]

There is a balloon over the boiler PRV pipe, with no sign of water discharge from there so I think the expansion vessel is OK

 

[Dotty]

OP. You're fishing for a definitive answer which we cannot give you.

Please read the forum rules and get a qualified person in.

 

[Dotty]

Another warning to new posters. Don't annoy the mods when your post is closed.