Furnace display shows flue gas sensor error; unit may shut down or run at reduced output

Safety: Turn off power and allow flue components to cool before touching.

• Locate sensor: Find the IVT flue gas sensor on the flue collector or near the combustion chamber outlet.
• Inspect mounting: Ensure the sensor probe is fully inserted into the flue stream and secured with its bracket or clip.
• Check wiring: Follow the cable to the control board, looking for heat damage or loose connectors. Reseat the plug.
• Measure resistance: Disconnect the sensor and measure resistance at room temperature. Compare to IVT specifications. Replace if readings are out of range.

Incorrect flue gas temperature readings can mask serious combustion issues; if in doubt, have a technician verify safe operation.