It will depend on the system used. We have what are known as the plans, S, Y, C, W etc. In the main the thermostat works a motorised valve and the valve has a micro switch which works the boiler. This can be built into the boiler or exterior to the boiler.
In the main oil boilers use C or Y plan as the heat in the boiler on turn off can heat the DHW, but where the DHW is done within the boiler often a W plan.
My oil boiler uses C Plan and has two motorised valve and two pumps, so not always easy to work out what you have, I now use oil in winter for DHW but solar in the summer, as can't turn off the oil heated DHW, if CH running it also heats the DHW.
I still have a problem with control, the hall with thermostat in cools too slowly, I really need a second thermostat in parallel but not fitted one as yet. What I want is a wall thermostat which will link to the TRV heads, that seems unlikely at a reasonable cost, but one needs to consider that before getting the wall thermostat, I made an error, I got Nest Gen 3 which I thought would work with Energenie but seems support was withdrawn when Google took over.
I note the sensor, but not read the instructions, the one I was looking at comes in three versions, electric, UFH and gas boiler with radiators, one does need to be careful to select the right one. I found
an instruction sheet here Seems I need a BHT-002 GC is for water/gas boiler. Even if it is oil. It says NTC is optional the sensors are used with under floor heating to stop the floor over heating when RAYCHEM electric is not used.
However one needs the read the instructions carefully. At £20 likely worth the chance it does not work, however I simply don't have the cabling where I want it, so only option for me is one with a sensor and base wirelessly linked.
Since it will for me be a second thermostat in parallel it does not matter if with a power cut power is lost, but as an only thermostat clearly needs to be powered from same FCU as rest of central heating.
