There is a cut out built into the thermostat,in the red and white plastic bit you will see a chrome tab sticking up just press and it will click if it has tripped,also to test the storage heater circuit put multimeter on the connector at the bottom with wall switch off it should read about 17ohms for a size 24 heater 22ohms for a size 18 heater 33ohms for a size 12 heater. I take it the supply is ok through the wall switch
toptrish
February 2014