Hello, I have a misbehaving boiler. It is a Worcester 240. The thing is every night when I'm just about to fall to sleep I hear what sounds like air knocking through my pipes in my bedroom radiator. It lasts anywhere between 5 and 15 seconds. It's been doing this for a few months and there is a back story which I'll go through. First off the boiler sprung a leak six month ago. It was a perished fibre washer. I replaced it and felt all smug. It was about this time I noticed the noise. Next I started losing system pressure. One morning I noticed the pressure was up near the 3 bar, I left a bottle under the PRV pipe and it filled up. Tried the valve on the expansion vessel and water came out so I fitted a new vessel. Left the old one in the boiler as I can't touch gas and fitted it external to the boiler. The system pressure stopped going high and my system stopped losing pressure. I felt all smug again. Until I'm just about to fall asleep and I hear this noise. What the heck is it? It is still happening even though the central heating is off on the front of the boiler but the noise is definately in the heating pipes. I should also say that I put the dishwasher on just before I go to bed (it's got hot and cold plumbed in) and I'm fairly sure the noise is coming when the dishwasher pulls in hot water and last night I noticed that a pipe into two radiators upstairs was warm at the time I heard the noise. Can't say if it is flow or return and it isn't on all radiators. The heating is not on. Does it sound like a diverter valve? Anyone know what's going on? Bit long winded. Thanks for reading and any advise. Pat.