Thanks very much Monika. I'm not sure about the insulation thing - if the house is left for a month and the heating has failed surely the temperature will be broadly similar to outside (or certainly way below zero if there is a prolonged cold snap)? Anyway, hopefully the electricity will not trip! We had a severe freeze up in 2003 including wrecking our water heater - it was my fault as although I had turned off at the meter i had forgotten to turn on the taps to empty the pipes! Hence the ballon installation