In have been running the cottage heating on tick-over (all the roomstats
set to 15 deg. C)
Yesterday I found the system had depressurised!

Apart from the panic about screws through underfloor heating pipes:-)
what would happen to a W plan system during a power outage?
The Veissman boiler has several minutes of circulation on the internal
pump and the system is happy with DHW thermostat reaching set
temperature and there being no call for room heating.

Based on the thermal expansion figures and discussion in here I
calculated that the vessel fitted in the boiler would do the job. There
was a fair bit of teeth sucking from the boiler installers but they
didn't offer any alternative calculations.

Looking at the sizing tables from the vessel manufacturers, I am a fair
bit under the recommendations. Could this be why?
--
Tim Lamb