There are Smart TRVs that can wirelessly trigger a contact closure that will turn on a zone for the boiler. You could also listen to the (usually Zigbee) protocol messages and close a relay yourself if you have a home automation setup (either directly from Zigbee, or by gatewaying the Zigbee to MQTT and then responding to the MQTT traffic).
The problem with running a call for heat to the boiler (nearly) full-time is that that will run the circulator pump for the zone and, if there's nowhere for that water to go (because all TRVs are closed and there's no "loopback" pipe), the circulator is going to draw a lot of power and eventually fail from being deadheaded.
> The problem with running a call for heat to the boiler (nearly) full-time is that that will run the circulator pump for the zone and, if there's nowhere for that water to go (because all TRVs are closed and there's no "loopback" pipe), the circulator is going to draw a lot of power and eventually fail from being deadheaded.
It's common to leave a single radiator without TRV for that reason - typically the bathroom.
I've found the TRV-less radiator is usually in the hallway as that's historically where a thermostat would live (ground floor, no windows, cool) and you don't want them to battle each other. You also want it to be sufficiently far from the boiler so the return water cools enough and you stay in/near the sweet spot for a modern condensing boiler.
TRVs are often avoided in bathrooms since those rooms have another source of heating (bath/shower) that will screw up what it's trying to do. Also, some smart TRVs don't have sufficient IP rating for such a moist environment. That said, you could install one in a bathroom and people do. Not sure why though, maybe they get carried away with their smart setup.
It depends on the circulator. If it’s the usual Taco 007, then yep it’ll fail. If it’s an ECM circulator set on delta-P like a Grundfos Alpha, then it won’t mind a bit.
The problem with running a call for heat to the boiler (nearly) full-time is that that will run the circulator pump for the zone and, if there's nowhere for that water to go (because all TRVs are closed and there's no "loopback" pipe), the circulator is going to draw a lot of power and eventually fail from being deadheaded.