After a couple of hours of the central heating coming on we sometimes get hot water pouring out of of one of the overflow pipes in the back garden. We have two tanks in the loft which both have connected overflow pipes. One is for water and I asumme the other one is related to the central heating. The smaller tank (related to the central heating) is the one which suffers from this problem. The tank is supplied by cold water which is attached to a ballcock and another chopper pipe which hangs over the tank. The water level is fine as the ballcock level is around 5cm below the overflow tank. What is strange is that the water in the tank is hot. I can only assume that the overflow is being 'tripped' by the pipe which over hangs the tank. I'm not 100% sure what the pipe is but I believe it must be connected to the central heating. Could it be that the boiler is producing too much hot water and is using the tank to get rid of the excess hot water ? This would explain why the water in the tank is hot and why the overflow is being tripped even the the ballcock level looks ok ? How do we prevent this from happening over then not running the heating ? We have tied turning the temperature down using the gauge but the problem persists. Any pointers ? Cheers !