In article ,
YAPH writes:
On Sun, 26 Oct 2008 22:23:45 +0000, asalcedo wrote:

I have installed two new Worcester 30 CDi system boilers at home. (They
work in tandem, at the same time, as if they were one unit)

According to the user's manual, under "Tips for Energy Conservation",
if the property has TRVs and room thermostats (which is my case), the
boilers should be set at the maximum temperature setting and use the
thermostats and TRVs to regulate the temperature as needed in each
room.

I certainly agree that that arrangement gives the most flexibility.
However, based on my reading of condensing boilers, the most condensing
and thus, the highest efficiency is achieved at 55 degrees Celsius.

If I set the boilers to the maximum the boiler's water reaches about 92
degrees.

If I use a 5 setting, 7 being the maximum, the boilers' water is about
62 degrees and still gets the house warm enough (at least now that it
is not too cold outside)

What is then the most energy efficient setting?

I think the user's manual is wrong in this respect. As you percieve, the
lowest possible flow temperatures which actually keep the house warm will
result in /marginally/ greater efficiency. Note that condensing boilers are

Agreed.
Most efficient is to set the boiler temperature low
enough such that the room stat never quite switches off.
That's the coolest water setting you can get away with,
which equates to highest boiler efficiency. The setting
will vary according to outside temperature (which is where a
temperature compensation system wins through), and it will
need boosting when the house is being heated up from a
temperature below the thermostat set point. A good control
system will do this all automatically for you.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]