H/W Cylinder fills Header Tank

[CPROSE]

Hot water is flowing from the hot water cylinder into the header tank through the header pipe (reverse flow).
No water is passing through the expansion/overflow pipe from the top of the cylinder into the cold water header tank.
The expansion/filler tank for the central heating is constantly refilling.
Any comments suggestions will be gratefully recieved, thank you.

 

[DeltaT]

If your header tank & F&E tanks are at different levels, then this can happen when your cylinder coil is knackereed.