Header tank in c/h system fills with hot water through vent pipe.What is wrong?

I havehad the system drained down,but problem persists.

Header tank in c/h system fills with hot water through vent pipe.What is wrong?
This is called cross circulation,check the pump speed,it might be set to high or there could be a partial blockage in the close proximity pipework.The system might be over heating.


Best to get in a heating engineer.
Reply:Reduce pump speed and CAP it off with a stop-end fitting, you wont do any harm.


The reason for "pumping-over" is the pump is too powerful, you must rectify this as soon as possible otherwise the tank will collapse as it is plastic, and boiling water will go through the ceiling, a baby was killed recently because a tank collapsed.


The other serious reason is that the water is being oxygenated, and this will corrode your radiators.


These overflows are specified by inspectors as a safety measure, in fact the system is already open to the atmosphere via the tank.


I HAVE CURED DOZENS OF THEM
Reply:coil leak
Reply:It is possible that some water may discharge into the tank that's why it is called a 'feed and expansion' tank. When the system gets hot and the water expands, the vent pipe discharges into the f.e. tank; and when the system is cold and the water contracts, water from the tank tops up the system.


This is a closed system, and the only way a f.e. tank can overfill is if the water inlet valve [ball valve or similar] is leaking.


There is an outside possibility that the calorifier [heat exchanger] in your hot water tank is leaking hot water into the boiler system, which might then have the effect of constantly overfilling the system. This would mean replacing the hot water cylinder.