Im looking at an intec 24x with pressure loss ove was couple…

Im looking at an intec 24x with pressure loss ove was couple days which increased to twice a day i sealed a few weaps on rads checked rest of system all looks good. Prob persists next checked expansion vessel for water coming out as i deflate small pressure that was in no water put bit of air back in and changed the pressure relif valve still same. Looked more into vessel disconected and pressurised to just ove 1 bar left for half hour checked and was same pressure reconnected refilled same prob. Reserched more and was sugested that reaction with system water and rads corrosion can create hydrogen amongst other gasses also the pump set to high same efect the gas escapes from auto air vent so turned the pump to low and filled system with inhibiter fernox left running yesterday seamed fin thus mor cold pressure 0.5 bar now @68degrees 2.3 bar ? Out if ideas without changing expansion vessel help

Contractor's Assistant: How long has this been going on? And how severe is the problem?

Months but was prob once a week / 1every two week top up before

Contractor's Assistant: Do you plan on doing the work yourself?

Well i am an intermediate experianced plumber and have a friend that is a gas engineer he is the one that said just replace expansion vessel but this is for my grandparents and they dont have money to throw around and as i tested it thought is was a waste of £120