Furnace runs but room never reaches set temperature, especially in cold weather

Safety first: Adjust only user-accessible settings unless qualified.

• Increase flow temperature: Raise the central heating flow temperature on the furnace within safe limits.
• Check thermostat calibration: Compare thermostat reading with an accurate thermometer. Replace if significantly inaccurate.
• Weather compensation: If using an outdoor sensor, adjust the heating curve to provide higher flow temperatures in cold weather.
• Heat loss assessment: A heating engineer can assess whether the furnace is correctly sized and recommend upgrades if undersized.