Can I install a thermostat to combi boiler?

I have a Vokera combi boiler (12 years old I think) but it doesn't have a room thermostat. It can be set on or off on the boiler itself and has a turning knob to adjust the temp but we can't set the room temp. We would like to fit a thermostat so we can leave the heating switched on all day and the room temp stays the same and we don't waste gas. Can this be done?