Programmable TRVs

In theory. It would probably be bulkier as well as more complicated and expensive, even if you integrated it rather than actually clamping onto the outside of a standard TRV.

No, it could set different temperatures by having the motor turn the control by different amounts, just as you do when changing the setting manually on a normal TRV. (It never really turns off, just turns the temperature setting down to 5C/frost protect. The boiler and system pump might be off, but that's separate.)

For even more complication, once you had reduced the power requirements, you could stick a heatsink and thermelectric generator in it to power it from the hot water without batteries or wires :-)

That could well be a bit of a problem.

Although I am usually at home all day, I have been surprised for how much of the year it remains perfectly comfortable to have the heating off from about 8 am until 4 pm. If it gets really chilly outside, the living room gas fire is probably more economical than firing up the boiler.

Chris

Fair comment. The best you'd get though is open loop control - whereas I presume that by motoring the valve in response to temperature changes, you can get closer to closed loop control.

An interesting thought! You'd have to somehow ensure that when the system shuts down, the valve is fully open - otherwise when it starts up again there not be any hot water flow to power it!

I was imagining you would want a supercapacitor (or rechargeable battery) so that a slow steady power from the generator could be matched to the intermittent load from the motor, so that would handle startup (at least to some extent, maybe not the first one of the year). (And it wasn't a serious suggestion.)