Has anyone controlled heating from 24V instead of mains?

I love the idea of the WiFi MQTT control relay and how it integrates with the emonPi. However, this seems to work by controlling the mains supply to the heating system, whereas my boiler provides a terminal block with three wires: 24V, control, and GND:

I checked the voltages weren’t dangerous, then bridged the control line to 24V with a 5k resistor and heard my boiler come on. So, with a 24V relay to switch the boiler on and off, I will be able to control my heating. This is to me preferable to switching my boiler’s mains supply on and off, not least because the only place I can access it is in my house’s switch box.

So, my question is: has anyone managed to do this, and if so, have they managed to link it to the emonPi? I see that the emonPi comes with OpenHAB and Node-RED, and I think some combination of those tools will allow me to control my heating in a smart way using existing temperature nodes in my house.

I’m not against the idea of designing my own circuit, but maybe someone has done the hard work already.

Follow-up question: I wonder whether it’s really necessary to use WiFi for this, like in the MQTT control relay sold in the shop. Is it not possible to use the existing 433 MHz network created by the sensor nodes? Could the emonPi send out “on” and “off” commands to a simple node connected to this 24V terminal? Then, you could still control it from your smart phone / away from the house by providing access via the emonPi.