I have noticed a problem with my power usage today. I'm watching the meter often and making a record of each reading for the last three days.

So far, nothing to note as far as unusual usage until this morning after being out.

I was gone for 2.5 hours and upon my arrival, I record the meter's display. To my surprise there was 13 kWh usage during the time I was out.

Over the last three days, myself and one other person have been using all appliances as normal (range, washer and dryer, air), bathing normal etc, and have only been using approximately 1.5 kWh (per average).

This morning the temperature was 19 degrees Celsius. The thermostat was set to cool at 21 deg/C. Beside the thermostat being set above the range of the ambient air temperature, I have no reason to believe the usage should be higher than the previous ten hour span, sleeping with air on.

In what way can I begin to troubleshoot this erratic power consumption?


By the process of elimination, I have found that the hot water heater is cycling excessively. However, it is not an issue with the tank maintaining the set temperature. It is an issue with water being circulated in the plumbing somehow.

If I disconnect the power to the tank, any excessive power consumption goes away, but I quickly (2 hrs?) loose the heated water in the tank. If I disconnect the water at the street, my power usage returns to normal and I can let the tank sit all day long and then still have hot water when I reconnect everything.

It seems likely to me that on the particular day that I asked this question - there was simply an inordinate amount of cycling while I was away. FWIW, this is a 120V water heater, so it seems possible for that usage to have occurred in that small time period.

  • Do you have a pool, spa, hot tub, sump pump, etc. that would only run occasionally?
    – Tester101
    Apr 15, 2014 at 11:44
  • Was anybody else home while you were out?
    – Tester101
    Apr 15, 2014 at 14:18
  • 1
    Solar gain can drive temperatures up well above ambient, causing the air con to kick on. Two hours during the day could be more cooling than ten at night.
    – bcworkz
    Apr 15, 2014 at 17:42
  • @Tester101 No to each device and no-one else was there.
    – Gabriel
    Apr 15, 2014 at 20:58
  • 1
    My guess would be that you made a mistake on your meter readings: easy to do. Track it over the next few weeks and see what happens.
    – getterdun
    Apr 19, 2014 at 0:38

1 Answer 1


Find the water heaters relief valve drain pipe and put a bucket under it. if this repeatedly fills with water the cause of the cycling and the lost hot water you are having is from two possible causes. 1. A defective relief valve that is popping open when the water is being heated causing it to be refilled with cold water. Hint to this is when the water to the home is off you have no problem keeping the water hot. 2. The water pressure as it is being heated is rising due to thermal expansion. I had this issue when I replaced an old failing water heater with a new hi efficiency one. The water pressure coming into the house from the city was 80 psi. With the new water heater I put in problems started due to the fact that water expands when heated and our water meter has a built in check valve to prevent reverse flow. The pressure would climb until it hit 150 psi and this would pop the safety valve causing it to return to about 90 psi. This would happen every time the water heater ran. The fix was to place a pressure reducer in the line to the house and install an expansion tank.


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