Re: Software will eat everything... sometimes
Newer boilers seem to support a 12V control line. Mine that is now 6 years old does.
Sending 240V to a controller is kind of crazy but convenient and I learned the painful way the first time I upgraded the thermostat in my current house with the old boiler
The Nest thermostat supports completely wireless with USB power or repurposing the disconnected 240V cable to provide 12V and power to the thermostat in which case you do not need the USB power supply. The boiler control/switching unit supplies the 12V from dedicated terminals
I have had a Nest thermostat for a few years now and it does seem to have reduced my gas usage. If only the cost had gone down too!