On Thu, 20 Aug 2009 09:51:43 +0100, "dennis@home"
wrote:

The longer/bottom heater will be used at night on economy 7 (if it still
exists) to heat the whole tank.
If you run low you use the top one to heat a bit at the top on full rate
electricity.

We always have plenty of HW left at the end of the day. Perhaps I
should use the top one on economy seven to just warm half a tank?!