hi the overflow for hot water tank in loft is constantly dripping, i have checked the float valve and that seems to operate as it should so any ideas what it could be and how to fix this problem.
Just to confirm, you are talking about the smaller of the two tanks in the loft?
When the heating water is cold the level should be about 4cm above the lower output; the ball valve arm should be bent to set the level. It is important that the valve opens before the level drops to the top of the outlet pipe, otherwise air can enter the system. The level will rise as the water is heated, but should stop well below the overflow. If the level continues to rise, the coil in the hot water cylinder is probably split or holed.
after taking another look yes it is the smaller tank in loft (hot water) and the level is correct when cold, other info i found out today is that when hot water cylinder is on hot water comes up vent pipe and flows into tank but the level rises but does not overflow. but when vent water stops and cylinder is off the water in tank slowly rises and then overflows. do you still think this would be the coil