Depends on the machine. Many take more hot water from the hot draw-off
than
others. Even if a machine only occasionally takes in hot water it is
still
well worth it as electricity is 4 times more expensive. That is a hell of
a
difference.

Which drops to nothing, or even negative when the wash fill is only a few
litres, which is probably greater than the amount of cold water that is
required to be flushed from the supply line.

If you have a water meter, the cost of the wasted water may be at least as
significant as the heating costs.

Yes electricity costs 3 to 4 times as much. However, the electrically heated
system will be considerably more efficient, mitigating or even reversing
this.

Some dishwashers can be hot or cold fill. Best hot, as it is still
cheaper
even though the rise is on hot.

Hot fill dishwashers do not clean as effectively as cold fill. Hot fill ones
use considerably more energy, as any rinsing cycles are done with hot water,
rather than cold. The supply pipes get hot and cool down several times in
the cycle, leading to much greater parasitic losses. That is why every
single 'A' rated energy efficiency dishwasher has cold fill.

Christian.