On Sunday, 29 December 2019 13:01:26 UTC, Tim Lamb wrote:
Probably much covered but a fresh issue for me:-)

Viessman modulating system boiler. Reasonably well insulated house.

Underfloor heating controlled by 10 (yes 10) thermostats and DHW given
priority.

In the excitement of moving house, I hadn't given much thought to time
clock settings and left 24 hour operation selected. With the relatively
warm Winter weather I have realised that the boiler spends most of the
burn time on the lowest of the 5 available settings.

Does this matter? I can cheat by limiting the CH on periods to provide a
bigger load. Any thoughts?
--
Tim Lamb

A constant low burn will be more efficient than on-off-on-off.
If only by eliminating the post and pre burn "purges" of cold air through the boiler.

https://idealboilers.com/support/faq...fan-post-purge

https://www.gobdc.com/purging-airflo...tion-required/