I have a Vaillant EcoMax Pro condensing boiler and also a Superduty fast
recovery hot water cylinder. When the boiler was installed the installer set
the boiler temp to 65C. A year later, a different guy from the same firm
came round to do the 1 year warranty check and insisted it should be 70C.
What is the optimum value, if there is such a thing? Or would I be right in
thinking that it's the return temp that's more important, and that it should
be 55C or less?

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?

Ta,

Steve S
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