Low burn is its most efficient mode.


From a total gas consumption POV I was wondering if running a boiler
for long periods at low output/high efficiency is better than drawing
the same total heat output but over a shorter period.

Off must use less gas:-) The house will be kept heated 24 hours anyway.


Surely, that's what 'most efficient' means? I know nothing about boiler
efficiency. This is purely a semantic point.