Ok, given that I have very few TRV's, and instead a series of fan
assisted convectors, how do you think I should control THAT lot :-)

I'd have thought that fan convectors would have simplified matters.

Wire OR all the room stats together to control the pump? And then what
about the rads with TRV's on?

If I had several fan convectors and several TRVs and didn't want a room stat
in the radiator part of the house, I would:

1. Have a programmable room stat for each fan convector (basically because
you can, and it gives separate timing for rooms likely to be used
differently, such as kitchens and conservatories, where such heaters are
typically installed).

2. Put all the convectors on a separate convector zone (or unzoned, if the
convector has an internal valve to prevent water circulation when off).

3. Put all the TRV radiators on the unzoned circuit, with flow switch. Any
bypass is before the radiator circuit

4. Run boiler when either HWC or convector zone valve (internal or external)
opens, or when flow switch activates.

5. Run pump either continuously, or when any zone valve or flow switch opens
and pulsed every ten minutes when not.

Alternatively, if the convectors have internal valves, an alternative is to
just treat them like a TRV radiator, in that they would cut the flow when
off and can activate the boiler using the flow switch, just like the
radiator. This would be very simple to wire, as the signalling to the
central heating from the convector is simply through the water pipework. No
electrical connection is needed.

Christian.