I think the thermostat on the heater is busted, as the water is scalding, is it okay to continue to use the immersion until I get the chance to replace it or should I switch it off until then?
Should be OK, but the thermostat is really cheap and very easy to replace. My advice would be to turn the immersion heater off and take the thermostat to B&Q or Wickes and get the same type and length on the spot...........