Nest Thermostat to Control Electrical Device

I'm looking to start a project and not sure if this is feasible with the arduino.

I have a Nest thermostat to control my home heating, but my kitchen has an electric underfloor heating element which has it's own thermostat. I'm looking to control this underfloor heating in sync with my nest and had an idea of how to use an arduino to make it work.

The nest I have is a UK model, so it controls a 'heatsink' (Learn about Heat Link for Nest thermostats in Europe - Google Nest Help) device which is basically a wireless relay which turns on a signal wire connecting to the boiler. (240v, max: 3A) I was hoping I could use this signal wire to connect to an arduino (have to step down from 240V i guess?) and use the arduino to turn on another relay which switches my underfloor heating on. The underfloor heating has a temperature probe as the element cannot heat higher than a certain temperature (safety) so I would also need to connect the existing temperature probe (2-wire, analogue I guess) to the arduino and program it so that if the nest is on, and the temperature is below the max to turn on the relay, otherwise turn the relay off.

I'm a fairly competent programmer in C# (web-backends) but the real world scares me. I'm not afraid of giving it a go, but is my project something feasible? Or have I missed something really obvious?

I think you are already in way over your head and advice would be to get a qualified electrician to run a link control cable and perhaps interface relay(if allowed by the electrical standards)

jdamner:
I'm looking to start a project and not sure if this is feasible with the arduino.

I have a Nest thermostat to control my home heating, but my kitchen has an electric underfloor heating element which has it's own thermostat. I'm looking to control this underfloor heating in sync with my nest and had an idea of how to use an arduino to make it work.

The nest I have is a UK model, so it controls a 'heatsink' (Learn about Heat Link for Nest thermostats in Europe - Google Nest Help) device which is basically a wireless relay which turns on a signal wire connecting to the boiler. (240v, max: 3A) I was hoping I could use this signal wire to connect to an arduino (have to step down from 240V i guess?) and use the arduino to turn on another relay which switches my underfloor heating on. The underfloor heating has a temperature probe as the element cannot heat higher than a certain temperature (safety) so I would also need to connect the existing temperature probe (2-wire, analogue I guess) to the arduino and program it so that if the nest is on, and the temperature is below the max to turn on the relay, otherwise turn the relay off.

I'm a fairly competent programmer in C# (web-backends) but the real world scares me. I'm not afraid of giving it a go, but is my project something feasible? Or have I missed something really obvious?

What happens if the Arduino locks up with the under-floor heater ON?
How then does the "SAFETY" high-limit temperature probe turn the under-floor heater OFF?