On Fri, 14 Mar 2008 09:39:22 +0000, Steve S \(another one\) wrote:

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

This is my take on the settings.

If the boiler knows the difference between doing the HW and CH then the
best settings (IMHO) is HW max and CH as low as possible but still
capable of heating the house. I think the Vaillant does know the
difference if it is wired up correctly, but that may including using
proprietary controls.

If the boiler does not know the difference between HW and CH (almost all)
then I suggest setting the flow at about 10C more than the thermostat on
the HW cylinder, if that's not enough to heat the house then consider
adding more radiators. Typcically HW temps are sett to 55-60C so the
primary flow temp should be 65-70C.

HTH

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html