expansion tank vent pipe overflowing?

ok hold tight, the reason why your vent pipe is running over is bad system pipework design or having the pump to high in the system (low head) which causes it to recirculate and introduce oxyegen which can cause corrosion. Forget that till you get a combi which does not need a tank! hurray, the problem is your water level is too high in the tank and when it gets hot it expands and overflows. Very carefully bend or adjust the ball valve arm down till water just above outlet pipe (bale out surplus water)

Dave Notrich- the honest Plumber (thats why i'm not rich)
January 2008