Some initial observations on the use of smart trvs on all the rads. (Zero zoning)

[Mister Banks]

Thanks, what I've done is check the part numbers, it's as I thought, the valve body is a common part. That's the good news. The bad news is that the flow to hot water, ie with the valve energised, exits from the opposite side of the tee in relation to the mid posn valve. So it's either a drain down, or the the valve energised whenever the heating is on. Not best practice, I guess

No, you really want the valve to be energised for HW.

 

[SimonH2]

FWIW I decided as an interim measure to go the low tech route.
One room I'd fitted unused back boxes and conduit so it was easy to pull in some cables and hard wire. For other rooms I paired a wireless program stat (Salus RT510) with two receivers - one controls the rad valve, the other turns on the pump.
I've a thermal store, so can use a modulating pump and no bypass. At the rads I have Honeywell thermo-hydraulic actuators which are silent but slow.
Not perfect, but a massive step up in comfort (it's an awkward house to control temperature wise) and should do for a while until I make or find something better. TBH all the "smart" systems I've looked at so far have downsides I don't want to live with. I also have to consider the WAF and she can cope with a stat in each room.