expantion tank hot water overflow help please

[nickcamberley]

Hi I have a central heating system that is a Baxi boiler behind fireplace, a hot water tank upstairs and a cold water and expantion tank in the loft.
My problem is this when the room thermostat goes off, the central heating bangs like there is air traped in it, then it sends hot water up to the expantion tank, making it constantly drip out of the overflow pipe from the expantion tank. I have bled the rads and the pump which help reduce the problem, however does not stop it. It gradually just gets worse with time. Any ideas or suggestions. Or quotes to fix many thanks.

 

[Armo74]

If you are having to bleed your rads on a regular basis and your expansion tank is overflowing it could be a blocked cold feed from your feed and expansion tank because that would also make the system draw in air and make the tank overflow. But you should also check your ball valve in your feed and expansion tank to make sure it isn't faulty.To check for a blockage try holding a magnet near where the cold feed tee's into the main flow pipe from your boiler.