Can anyone help with a problem with standard central heating system? The problem is that water is coming back up the cold supply feed from the water cylinder into the expansion tank and overflowing even when the central heating is turned off and mains water supply is also turned off. When turning off the gate valve connecting the cold water return, water then starts coming out of the vent pipe.
Is this a split in the coil inside the cylinder? Or is it an air problem? Please help
Thanks James :)