Danfoss REP230 Thermostat Wiring?

Long story short, I have the above thermostat and had an installer try to replace it with the new NEST thermostat. It was faulty and I couldn't be bothered with the hassle of getting another one so I asked the installer to re-install my Danfoss.

It doesn't control the boiler at all (boiler doesn't go off when temperature is down low) and I've had an engineer out today. He told me he fixed it but alas it is still not working.

I noticed there is nothing connected to the "OFF" terminal. I am a complete lay-man with this but do you think this is the problem?