Hi, I have an older style open vented heating system with a Glow worm 50/60 RF flued fan boiler. I have a hot water tank on the first floor and two header tanks in the loft, one large for the hot water and a smaller one for the heating. Last week I removed a radiator from the landing and capped off the pipes under the floor. Since doing this when the boiler switches off there is a loud bang and the whole heating system shakes. I thought it was an air lock but I have bled the system and all radiators are warm. It only does it when it's on heating, not when on hot water. Another point, when the boiler switches off water runs into the header tank for about 3 seconds.p from the expansion pipe. I've even tried connecting the pipes I cut off together just in case I had messed up the flow and return but it's still the same. All radiators have trv's apart from a heated towel rail in the bathroom and large radiator in the hall which is by the thermostat. Anybody have an ideas what it might be. I have also flushed the system and it is clean. It's worked fine for years until I removed the radiator. Many thanks. Paul.