"Stephen" wrote in message
...

I had not realised that the top heater is only used for boost and the
bottom heater only used for overnight. I always thought they came on
together. I realise this is due to the cable again but it does seem
silly having a top heater that is never used.

The top heater is very good if you want a limited supply of hot water as it
doesn't heat the entire tank.
An example would be for a shower rather than a bath.


The heaters are controlled by something like this:
http://www.screwfix.com/prods/44419/...rtz-Timeswitch

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.

If you don't have economy rate electricity use the top one only for anything
that doesn't require lots of hot water, or get a gas heater.