Many thanks Roger for earlier answer. I have changed the wall switch this week but the switch is still heating up esp around the fuse. Electrician thinks it is something to do with wattage going through the heater. Looks like mains box has 20 amps going through to the off peak system but wall switch has 13 amp fuse. Does this seem ok?
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.