Hi , i have a grant combi mk11 oil fired boiler that started to get high pressures .This has happened before so i changed the expansion vessel .I checked the pressure in the vessel before i installed it and it was fine a 1 bar ,drained the system and then fitted the new vessel .It was ok for a few hours but has now gone back up to 3 bar
Has anyone got any ideas what the cause could be ?
Has anyone got any ideas what the cause could be ?