Hi, I called Dimplex (0845 600 5111) who gave me contact details of my local storage heater specialists.
Anyway, i called them out and they resolved the problem in under an hour. Basically the thermostats needed replacing (apparently this needs to be done every 5 or so years).
Heaters working fine now and only cost me £50 per hour call out + £28 each for the thermostats.
Tony
November 2008