I wish to replace an old Sunvic room thermostat controlling the coal fired central heating system. I have purchased a SUNVIC TLX 9201 thermostat. The existing wires are red, yellow, blue & yellow/green. The new thermostat has 4 connection points.(ie: they are numbered 1,2,3,4) Could someone please guide me as to where these wires should be placed-cheers!