"Mary Fisher" wrote in message
t...

"dennis@home" wrote in message
...


"Mary Fisher" wrote in message
t...

"Steve S (another one)" wrote in message
...


If it's the return temp that's important, then I have a supplementary
question... I understand that hot water in a cylinder should be heated
to 60C in order to prevent the growth of Legionella bacteria. Is this
correct, and if so, how do I reconcile the two requirements -- return
at 55C or less, but hot water = 60C?

The 60C is only for the first use, to 'kill' any harmful bacilli in the
equipment.

I wonder why you have to boil stuff for several minutes to kill bacteria
if an initial burst of heat will do the job?

The worry in water heting equipment is about specific bacilli.

What bacilli do you kill at several minutes of boiling? And how does any
central heating/domestic hot water system maintain boiling for several
minutes?

The correct answer is not many, it takes longer for most.
However you kill a lot of each type.