My hot water was coming on when not switched on, even when I removed the programmer, so I replaced the programmer (with identical one). Still had the same problem, checked in loft and zone valve was ceased. I replaced the zone valve, and when i turned fused switched spur on a little bit of smoke came out of new zone valve, and fuse blew. I checked whether the valve was open or closed and repositioned zone valve in correct position. Then when I turned the programmer on CH it worked, but as soon as I switched HW on it fused at the spur switch. Any suggestions as to what is wrong, I have been told that there may be a problem with a neutral on the PCB??