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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 :)

bit hard to be sure what you mean - assuming that you are talking bout the small central heating expansion tank and not the big cold water storage vessel, it does sound like a split coil.

if you turn the mains off and drain the big water tank (to save a long wait!!) (hot or cold tap in the bathroom) until the water levels are nearly the same, then check to see if these two tanks level out then you can be pretty sure that your diagnosis is correct.

In which case - "never mind" is an expression that springs to mind!

Hi James,

Sounds like the coil has had it.= new cylinder.