Furnace runs but delivers insufficient heat; home never reaches thermostat setpoint.
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: Gas pressure and combustion adjustments must be done with proper instruments. Homeowners should limit work to basic checks.
Steps to check:
- Filter and airflow: Ensure a clean filter and open registers so the furnace can move its rated airflow.
- Thermostat location: Confirm the thermostat is not in a drafty area or near heat sources that could cause premature cycle termination.
- Observe burner flames: Flames should be strong and blue. Very small or lazy flames can indicate low gas input.
When to call a pro: A technician should measure inlet and manifold gas pressure, verify correct orifice sizing for your Heil model, and adjust or replace the gas valve if needed.