I have only ever once seen this before and it was in a house where they were on old style fuses so it did not trip out, I had actually gone to fit a door seal as it had been leaking but after fitting it the machine did the same thing it took me ages to find it but the seal had leaked onto the heater and shorted causing a burn from the negative heater terminal down to earth and as the heater switched on the negative it became powered up all the time.
powerhousesteve@hotmail.com, November 2005