you must have a leak SOMEWHERE for it to lose pressure that quickly
have you tried checking the safety blowoff pipe?
if you have been over ''every inch of system'' [including pipework hidden under flooring, inside ceilings & walls?] & found no leaks then that would ''suggest'' an internal leak inside the boiler
OH DEAR!
you now require a qualified gas engineer to find & repair the leak inside the boiler
in my experience build quality on these French boilers is not fantastic & they are known to leak like sieves eventually
I have lost count the times I have been called out to ''boiler keeps losing pressure'' problems where the customer swears blindly that there are no leaks on the system only for me to find major leaks on underfloor piping & radiators [normally within the first 10 minutes of looking]
normally these leaks tend to occur after radiators have been removed & replaced during decorating OR when a carpet fitter has been going around the house hammering down loose floorboards prior to fitting new carpets & inadvertently puncturing heating pipework
Q
June 2015