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Tim Lamb[_2_]

In message ,
writes
On Sunday, 10 February 2019 19:33:38 UTC, Tim Lamb wrote:

what would happen to a W plan system during a power outage?

everything stops & goes out, except the pilot light if a boiler has
one. What is the unknown there?

Er.. whether the thermal energy in the heat exchanger is sufficient to
overpressure the system with no circulation.

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?

You can always leave some air in the top of a large enough radiator.

I could if there were any:-) Fully underfloor system. Curiously, I am
almost certain there is a second pressure vessel inside the thermal
store DHW tank.
--
Tim Lamb