I'm trying to fit a new central heating thermostat and I'm unsure of which wires go where could anyone help me please?

I have bought a sunvic digital room thermostat TLX 7501
With three terminals numbered 3, 2, 1, in the bottom right hand corner as you look at it.

I have four wires one yellow, one red, one blue and one yellow/green please could someone tell me which goes in where

You must be in the UK.

Here is the factory site.

Sunvic Controls Limited

I personally have never used one of these t-stats and have no idea what your color code is in your country.