Furnace runs but produces insufficient heat; home never reaches set temperature.

Safety: Gas pressure and combustion adjustments must be done by qualified personnel.

• Check thermostat settings: Ensure the setpoint is higher than room temperature and that any setback schedules are appropriate.
• Verify all zones are open: Make sure radiator valves or zone valves are open where heat is needed.
• Clean air and water side: Replace dirty air filters (warm-air models) and bleed radiators to remove air pockets (hydronic models).
• Schedule professional service: Have an Ariston technician check gas inlet pressure, burner condition, and perform combustion analysis to ensure the furnace is firing at the correct rate.