In article ,
"Suz" writes:

"Martin Angove" wrote in message
...
Since dishwashers have some quite hot programmes, why is it that they
usually only have a cold feed? Washing machines rarely come without a
hot feed, why not dishwashers?

Our washing machine has a hot and cold feed, but only takes hot water for a
boil wash. I suppose there could be a risk of too hot water hitting clothes
that can't take it. Or the cost of something that accurately measures and
adjusts hot/cold ratio on filling.

Modern washing detergents require a profiled temperature wash.
They contain various enzymes, each designed to break down a
different kind of dirt, but each with a different operating
temperature. For the enzymes to work, the water must be heated
slowly or in stages, allowing time for enzymes to operate before
going above the point where that enzyme is destroyed. They are
all well destroyed by 60C anyway -- they are intended to give
good results at 35-40C, and will work better on many types of
soiling than a 60C wash which relies on the detergent alone.

I have a microprocessor controlled Hotpoint, and that does
indeed mix the hot and cold aiming for a 30C fill temperature,
which is the starting point for the profiled temperature wash.
It starts with cold only, but then starts mixing in hot. If
the hot water actually isn't vert hot at all, it ends up
shutting off the cold and filling just with the hot.

--
Andrew Gabriel