siemens rdj10RF thermostat troubleshooting?

I have programmed th ethermostat to comfort temp 20 degrees and setback temp 10 degrees but the heating did not swich on when timed to do so and the room temp was 18 degrees so i presumed it should have worked! where should the slider at the bottom and on the left be positioned? i had it set on Auto at the bottom and run on the left? Any help would be good. Thanks