Please can anyone help.

I have a 7 day timer for my hot water and central heating. When I set the
timer for the central heating to come on, it does, but the hot water gets
hot...very hot (over 80 degrees)as well. No light on the timer comes on to
show the hot water is on. The hot water will come on with the timer when it
is set.

Having the hot water heat up everytime I have the central heating on is
causing the hot water to get very hot and the tank thermostat is not
stopping it. (For some reason there is a permanent live going to the
thermostat on the tank as well?) I have now burnt out 2 thermostats!

An electrician came to check the wiring in my timer and said it was all
fine. My plumber came several months ago and fitted a new motorized valve -
he put in a 6 wire one instead of a 5 wire (to replace the old 5 wire) -
there were no 5 wires available and he said it would make no
difference....BUT could this be the cause of my problem? OR could there be a
crossed wire between upstairs where the tank etc are and downstairs where
the timer is? Would a crossed wire cause the hot water to come on everytime
the central heating does?

Please help me someome. My plumber and electrician are completely stumped,
my daughter burned her arm badly in the boiling water and my gas bill is
rising!