Evening all, Need advice....I have recently purchased a house which needed lots of work doing. It has no mains gas so everything is electric, radiators and immersion for domestic hot water. The main stop cock has been off for about a month whilst refitting the kitchen and bathroom. A week or so again turned it back on and within a day or two I noticed that the cold water loft tank was overflowing. I replaced the entire ball valve unit and observed it working fine, closing the inlet valve when water was about 2 inches below the overflow pipe. Within a day or two noticed the overflow dripping again. Upon checking appears that the ball valve is working fine with no leaks or dripping whatsoever. The only other potential source of water is via the immersion tank expansion pipe which enters the cold water storage tank at the top, although upon checking this it appears dry. The immersion tank has not been changed or altered in any way, nor has the cold water tank (with the exception of the ball valve unit). The immersion heater element thermostat is set at 60 degrees and the water hot temperature when checked is coming out of the tap at about 56 degrees. Any idea what could be causing the problem?