Status LED flashes once repeatedly, furnace will not start heating cycle.
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 electrical power to the furnace at the service switch and shut off the gas supply before removing panels. Allow the furnace to cool.
This code usually indicates the control board did not sense flame after opening the gas valve.
- Check gas supply: Verify the manual gas shutoff valve to the Thermo Pride furnace is fully open. Confirm other gas appliances in the home work.
- Inspect flame sensor: Remove the burner access panel. Locate the flame sensor rod near the burner. Disconnect the wire, remove the mounting screw, and gently clean the rod with fine steel wool or emery cloth until shiny. Reinstall and reconnect.
- Inspect hot surface ignitor: Visually inspect the ignitor for cracks or white spots. Do not touch the element with bare fingers. If cracked or open (test with a multimeter for continuity), replace with the correct Thermo Pride-compatible ignitor.
- Check burner manifold and orifices: Ensure burners are not clogged with rust or debris. Clean with a soft brush and compressed air.
- Reset power: Restore power and gas, then call for heat at the thermostat and observe ignition sequence through the sight glass. If the ignitor glows but burners never light, suspect the gas valve or low gas pressure.
When to call a professional: If you smell gas, if the gas valve is suspected faulty, or if ignition still fails after cleaning the flame sensor and verifying gas supply, contact a qualified HVAC technician familiar with Thermo Pride furnaces.