LED flashes code 43; furnace may not respond correctly to thermostat calls, staging may be incorrect on two-stage Tempstar models.

Safety: Turn off power before adjusting control board settings.

• Step 1 – Verify thermostat type: Ensure the thermostat is compatible with your Tempstar furnace (single-stage vs two-stage). Replace with a compatible model if needed.
• Step 2 – Check dip switches: Refer to the Tempstar installation manual and verify that blower speed, staging, and comfort settings on the control board dip switches are set correctly for your system.
• Step 3 – Tighten low-voltage connections: Inspect all thermostat and accessory wires at the control board. Tighten any loose terminals and ensure no bare wires are touching.
• Step 4 – Test with jumper: Temporarily jumper R to W at the furnace to simulate a heat call. If the furnace operates normally, the thermostat or its wiring may be at fault.
• Step 5 – Replace control board if needed: If wiring and thermostat are good but the furnace still misbehaves, the Tempstar control board may be defective and require replacement.