I don't think it can go that low - the MI's say 7.9kW.[...] The Veissman 100 W compact would seem to modulate from 13kw max to 1/3 of that, ie 4.3kw.
Mathew
Thank you for pointing me to that.I am using the below, which may be different as it is described as "compact". It says that the boilers modulate down by a third, which may apply to the bigger ones as well, so they may not all go down to the same value.
http://www.viessmann.co.uk/etc/medi...e.Par.12469.File.File.tmp/DPGOCT2011_web1.pdf