I have just moved into a house with a Maxol Supercombi HE28 boiler, a Drayton Digistat +2RF thermostat/programmer and a Digistat SCR. The boiler has a mechanical timer. The only way I can get the central heating to work is by using the mechanical timer. The Digistat display is on and the 'flame' symbol is displayed. The green light on the SCR is on constantly. How do I get the heating controlled by the Digistat rather than the mechanical timer?