Looking at other answers, I think this is a thermostat issue, but would appreciate advice. My mother's two night stores, Dimplex XL18 and XL24 - installed 1990, normally use on average 30kW each night, on controlled night power supply, 8 hrs per night, set to between 5 and 7, when 9 is maximum setting. For the last two years, the usage has gone up, to average 55kW per night. Some nights, 120kW, last night, 74kW, other nights 95kW, with no obvious pattern. This is actually far more kW's than they are rated to use on full - how can that happen?? Her electrician is coming in to check them over tomorrow. The power company installed a replacement meter approx 2 years ago.

Cathy, July 2010

The answer turned out to be a dud meter, it hadn't been replaced two years ago after all, and luckily was installed on the night store heaters and thus isolated from general usage. After numerous emails/phone calls/letters, and a chat with the very helpful meter testing laboratory, the power company agreed to refund $1,000 of overcharging from the two previous winters. Apparently there was a dud batch of meters installed throughout New Zealand between 1989 and 1993, that could go haywire at any time, esp after having no load for a while. One meter on the test bench had clocked up 16,000kW overnight with only an extension lead plugged into it. Fortunately my mother had kept her power bills back to 1993 and we had a perfect record of her usual night store usage. The power company finally did admit to the meter being faulty, but we had to persist.

Cathy, December 2010

Thanks for the advice Steve. I'll put the result up when the electrician has been, to help anyone else having the same problem.

Cathy, July 2010

your`e correct the way to calculate it multiply KW rating by 7,[7] being the usual amount of time off peak is on. An XL24 is 34kw.an XL18 is 25.5kw to charge from cold so your average is about right. the heaters need to be checked first,the resistance of the 24 should be about 17ohms
the 18 about 22ohms give or take, even if stats were stuck its impossible to take any more than 60kw and the heaters would be glowing, hope this helps a bit

steve.e, July 2010