The pressure in the combi boiler steadily rises, over about 8 hrs, to 3.0 bar. I've had to keep on bleeding to bring the pressure back down. This happens even with the CH function switched off. I've checked that the filler loop is completely disconnected. I've also switched off, reduced the pressure right down and tried to repressurise the expansion vessel (this seems to slow it down but after a while it starts again). I can only get about 0.75 ish bar in the expansion vessel. Why is this happening with the CH switched off? It's been recommended that the expansion vessel is kaput. Any ideas on what else I can try?