Display shows Er2 and furnace shuts down or will not ignite.

Safety first: Turn off the furnace and disconnect power before removing panels or touching wiring.

Steps:

• 1. Confirm the error: Cycle power to the furnace. If Er2 reappears immediately, proceed with checks.
• 2. Locate the room temperature sensor: On many US Stove furnaces, the room sensor is a small probe or thermistor mounted on the front panel or in the return air plenum, connected by a two-wire harness to the control board.
• 3. Inspect the sensor and wiring: Look for damage to the sensor body, broken insulation, or wires pulled loose from the connector. Ensure the connector is fully seated on the control board.
• 4. Test the sensor: With power disconnected, unplug the sensor and measure resistance across the leads. Compare to the resistance chart in your model’s manual at room temperature. An open or shorted reading indicates a failed sensor.
• 5. Replace the room sensor if bad: Remove any mounting screws or clips, install the new US Stove room temperature sensor, and route the wiring away from hot surfaces and moving parts.
• 6. Check for wiring shorts: If the sensor tests good, inspect the harness from sensor to board for chafing against metal edges or contact with the firebox or exhaust components.
• 7. Control board check: If Er2 persists with a known-good sensor and wiring, the control board may be defective. Have a qualified technician test and replace the board if necessary.