my header tank has been overflowing for atleast a year and a half. i have tried many different things but to no avail. i have a back boiler in my dinning room and central heating and hot water run through this. my hot water tank is in a back bedroom with the pump next to it running vertically. the header tank is then above these in the loft. i have now began to wonder if the pump that is next to the hot water tank is pumping in the wrong direction. i have looked at the arrow on the pump and it is pumping up towards the header tank. could this be the cause of the overflowing tank? methods i have tried to sort this out have been to clean the entire system with fernox i have taken half of the radiators off the walls and flushed them through and also changed the ballcock in the header tank incase it was broken and letting too much water in none of these have worked