Replacing room thermostat for central heating

[canetoad]

Hi,

I have a Honeywell radial dial thermostat inside my front door for the heating and wanted to replace it with one with a digital display. It has 4 wires running to it, earth, live, neutral and one extra, which I'm not sure of. I bought a DT200 from Screwfix to replace it but it only has a live and neutral connection. There is a third terminal but it's covered with a plastic tab.

Can I use the DT200 (also Honeywell) and, if so, how should I wire it? If I can't use it what other model could I fit?

Just discovered the 4th wire (yellow) is switched live.

 

[mogget]

The four wires on the old stat will be live, switched live, neutral, and earth.

The new stat doesn't need a neutral.

Live and switched live go to the 2 terminals on the new stat.

Neutral needs making safe (terminal block), and there's often a 'convenience terminal' for the earth - put it in a second terminal block if not.