I am reasonable at DIY however having a problem in wiring up a new room thermostat to my new boiler.

The boiler (Ravenheat Little Star) only has two connections for room stat and the stat (Drayton Digistat 3) has 3 connections.
Can anyone help with what connects to what.

I've rewired the house with no problems but this has me a bit bewildered.

Any help would be gratefully received

Mark