On 04/11/2020 09:00, harry wrote:
On Tuesday, 3 November 2020 18:32:31 UTC, Tim Lamb wrote:
It is that time of year...

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C. My thought was that it
does not leave much room for DHW at 60deg. to avoid bacteria.

My flow and return piping is insulated so there should not be much
loss tank coil to boiler.

The other question I have related to weather compensation. My
system boiler has provision (not fitted) for this but no other
arrangement for reducing the set temperature when running the
underfloor heating. The manifolds have local thermal control valves
but it seems daft running the boiler at 65 when 55 would be ample.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

This weekend is *move the by-pass valve* event!

The purpose of "weather compensation" is to anticipate increased heat
load by means of an outside temperature sensor.

Yup, although most I have looked at are reactive rather than
anticipatory... not quite sure how you would do an optimising weather
compensator.

So if it get cold outside the heating is boosted before there is any
fall in temperature indoors.

The amount of "boost" needed depends on the house
construction/insulation. May or may not be adjustable.

On my system, its by choosing a response curve:

http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png

I believe the Viseman system boilers also use a similar approach.

On the Vaillant setup it also factors in the set point internal temp
shifts the whole curve up to force higher flow temperatures if the
temperature is set higher :

http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png

So in this case it actually works the way many people think a thermostat
does - turn it up higher and it *does* heat up quicker! :-)

--
Cheers,

John.

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