Fairly new condensing boiler (with hot water tank). Went on holiday. Left boiler 'on' for C/H and off for hot water. Hallway thermostat at 14c. On my return, house seemed cold. Heating had not clicked in. Checked programer. (hall thermo was clicking ok) . As last resort I slightly moved the thermostat on the boiler by 2mm clockwise & it came on. Problem solved I thought, as I presumed it had overidden the hall thermo. Later on I came back & again the heating had not clicked in. Upped the hallway thermo - clicked, but no response. Then upped the boiler thermo again to nearly max (even though the recomended max is about two thirds round) - no response. As last resort, turned on the water to 'on' and not only did the water start heating but the radiators started getting warm as well !! Last couple of days no problem, but this intermittent fault is of concern to me if I am away again. Any ideas ??