boiler losing pressure

[tarb]

baxi boiler losing pressure every few hours
no visible leaks apart from condensing pipe running had expansion vessel and prv valve replaced which helped for a few days .been told heat exchange may be at fault so need new boiler
can any one give second opinion please

[gas4you]

Pressurise the boiler and isolate the boiler from the heating system via the valves under the boiler. If pressure remains stable then leak is on the boiler, if it drops it's on the system somewhere.

If everything else has been eliminated and there is water constantly running or dripping from the condensate then it points to the main HE having a pin hole or similar in it.

[tarb]

Thanks for the reply
Do I turn the heating on after I’ve isolated it

[gas4you]

No just leave the boiler doing nothing for as long as possible.

Although they have replaced the expansion vessel I also wonder if the pipe connecting it could be blocked.