I know the heaters do not run together, but whilst the immersion runs you are
either waiting for it to heat up, or cleaning with cool water.
If on a Powrflite or other heat exchange machine, you want the tank warmed up
then run water through the exchanger and a short pipe from the outlet, back into the tank, this means your immersion heater
is superfluous, and just added to the cost of the machine. The older Ninjas had a bypass valve, to do this. Ashbys don't like the
tank too hot, which is why they removed this feature.