Can anyone help - some general advice needed please. I've just moved and i'm trying to work out how the CH/water system works. The oil boiler is housed in an unheated outside room (at the back of the garage), there is a manual dial type thermostat on the wall in this room which appears to go from -10 to +15. There doesn't appear to be a wall mounted thermostat in the house. All the radiators in the house have TRVs. It all appears to be controlled by a Potterton EP2000 timer. So do I assume that the boiler is controlled by the air temperature in this unheated outside room (presumably why the wall thermostat appears to have a very low temperature range compared with one you would find inside a house) and does that mean when it comes on is governed by the temperature outside the house rather than inside? Any help appreciated.