Heating expantion tank slowly backfilling

[phil247]

Hi
My expantion tank is slowly backfilling, it fills through the pipe at the bottom of the tank, obviouslly this is meant to do this hence expantion tank, but it doesn't stop and overflow's. this only happens when the heating is on and not when the hot water is on. it's a recentlly fitted boiler with a two way motorised switch between water and heating. this has the plumber who fitted it baffled and to be honest that's not filled me with confidence. if it's a hole in the water tank coil wouldn't it overfill all the time and would our hot water be contaminated with heating water?
any solutions or ideas would be much appretiated.
Regards
Phil[/b]

 

[chrishutt]

With certain pumped circuit arrangements the closing of the motorised valve on the flow to the cylinder coil will subject the coil to a reduced pressure caused by the suction effect of the pump. When the coil pressure is reduced there is a greater tendency for water to leak from main body of the cylinder into the coil. Your symptoms are therefore consistent with a leak in the cylinder coil.

 

[phil247]

Cheer's Chris, looking at getting a new tank now. let you know how i get on .