Furnace runs but does not produce enough heat; home takes a long time to warm up or never reaches set temperature.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Gas pressure and orifice sizing must be checked by a licensed technician. Do not attempt to drill or modify orifices.
Homeowner checks:
- Verify thermostat setting and schedule: Ensure setback schedules are not too aggressive and that the thermostat is properly calibrated.
- Check filter and registers: Replace dirty filters and open all supply registers to maximize airflow.
- Inspect for duct leaks: Look for disconnected or leaking ducts in accessible areas (basement, attic). Seal with mastic or UL-181 foil tape.
Professional checks: A technician should measure temperature rise across the furnace, verify input BTU by clocking the gas meter, check manifold pressure at the Coleman gas valve, and confirm correct orifices for the fuel type.