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from fred contains these words:

3. Should I just do the two north facing rooms?

4. Or three zones... North facing up, south facing up and downstairs?

5. Or one zone up, one down...

4 zoning would seem like a reasonable split, 2 up & 2 down. Reasoning
downstairs being why heat the kitchen at all when you're watching telly?
Upstairs is probably less in need of a split but it shouldn't be too hard to
do. Separate zones really are superior to the sort of results you get with
TRVs.

I initially resisted the idea that I would benefit from zoning as I have
an open staircase leading from the living room but I eventually weakened
and have not subsequently regretted it. FWIW I have effectively 3 zones.
Downstairs with the programmable stat in the living room, upstairs with
the programmable stat in the main bedroom and the bathroom where the
radiator (with a TRV) is on the boiler bypass circuit and is thus
supplying needed heat whenever the boiler runs. There is an automatic
valve on the bypass circuit which can operate when the bathroom TRV is
closed.

--
Roger Chapman