It is best practice to have the boiler turned up to max heat and in the timed position. With the Wall mounted room thermostat set to 18*C or 21*C depending which room it is located. Then have the TRV's (Thermostatic Radiator Valves) set to number three.
If the radiator has not been sized correctly for the room then it may not be able to cope with replenishing the heat loss and it will never get warm enough in the colder months. Same goes for the boiler it also should have been caculated and sized correctly to be able to cope with the demand, dimensions and fabric of the building.