Hi, i recently had an issue with losing pressure on my boiler. A plumber came round and carried out a power flush and replaced a PRV, he also added a Magna clean filter and checked the expansion vessel which he said was OK. This sorted the issue for about a month. I now have the opposite problem. When the system is off the pressure is very stable, it is also fine when the hot water timer kicks in for an hour or so in the morning. However when the heating comes on the pressure rises well into the red zone. (Regardless of whether the hot water is on or not) The plumber came round and checked the expansion vessel and said it had pulled more pressure (which i thought was strange) and corrected it to 0.75 i believe? The same issue is still there regarding the pressure raising when the heating is on. Any advice would be great.