Tools You’ll Need for the Job 4-In-1 Screwdriver If the flame sensor does not detect a flame, it will also cause the furnace to shut off.Ĥ1K5601 - Lennox OEM Replacement Furnace Ignitor Igniter If the ignition process delays, it will cause the furnace to shut off. However, if the control board is defective, it may not be sending power to the ignition system, which will prevent the furnace from remaining on.Ī defective pressure switch, which means it isn’t closing when the burner has sufficient airflow, could also be causing the firing-up process to delay. The control board sends power to the ignition system, which fires up the system. If the furnace fires up but then shuts off after a few minutes, it could be that the control board is faulty. If the flame sensor does not detect a flame, as a safety precaution, the control board will shut off power to the gas valve to prevent the furnace from heating. A dirty or faulty pressure switch, which monitors the burner to detect a flame, can also cause the furnace not to produce heat. If the igniter fails, it will also cause the furnace not to produce heat.

If you arrive home or arise in the morning to a cold house, it could be that the thermostat is set on a low setting, which can cause the furnace not to put out heat. Sometimes a circuit may have tripped, which can also cause the unit not to start. In this case it will need to be exchanged for a new one. Sometimes, either the thermostat has been switched off accidentally, or the thermostat has completely gone out. If your furnace just stopped working, it could indicate an issue with the thermostat.

Lennox Furnace – Common Issues The Furnace Won’t Start

Old lennox furnace parts