On Wed, 12 Jan 2005 22:34:49 +0000, Gaffar wrote:

Christian McArdle wrote:

Could someone please explain what a fully modulating combination
boiler is,

A fully modulating boiler is one that can vary the heat output according to
demand. A combination boiler is one that incorporates a hot water system to
supply taps. Most combi boilers are of the instantaneous type.

It is essential for sane operation that such instantaneous combis are fully
modulating. Otherwise, turning the tap down will cause the temperature to
rise until the boiler decides it needs to cut out, turning the water cold. A
fully modulating type will just turn down the gas to keep the temperature at
the set point.

Christian.

Thanks for the simple explanation, the concept is at least understood
now.

I have finally received the installation ans servicing manual from
Vaillant and in it, although there is nothing explicit which says that
it is fully modulating, there is a section for fault finding of which 1
sheet is headed "check burner modulation" would this indicate that this
boiler is fully modulated, or am I way off the mark


I'm nigh on certain that all Vaillant combis are modulating.
I think there may be some very early Vokeras which aren't.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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