Furnace runs but produces no warm air; blower operates, but supply air is cool or only slightly warm.
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: Turn off power before removing panels. If you smell gas, shut off gas at the main valve and call your gas utility or a professional immediately.
- Check thermostat settings: Ensure the thermostat is set to HEAT and the setpoint is above room temperature.
- Verify gas supply: Locate the manual gas shutoff valve near the furnace. The handle should be parallel to the pipe (ON). If perpendicular, turn it parallel.
- Observe ignition sequence: With panels on and power restored, watch through the sight glass. You should see the inducer start, ignitor glow, then burners light. If the ignitor never glows, it may be failed. If it glows but no flame appears, the gas valve or gas supply may be at fault.
- Check for error codes: Look at the Carrier control board LED through the viewing window. Note any flash codes and address them using the furnace's label or a professional.
If the furnace repeatedly tries and fails to light, shut it down and have a technician test the gas valve, ignitor, and safety circuits.