Daikin furnace shows A1; unit may not respond to thermostat commands or may lock out.

Safety: Disconnect power to the furnace before touching the control board or wiring.

Steps to check:

• Visual inspection: Remove the blower door and locate the Daikin main control board. Look for burnt spots, bulging capacitors, or a burnt smell.
• Check connectors: Gently press on all multi-pin connectors and terminal blocks to ensure they are fully seated. Look for corrosion or discoloration on pins.
• Check for water damage: Inspect above and around the board for signs of water leaks from the flue, humidifier, or coil drain pan that may have dripped onto the PCB.
• Power cycle: Restore power and see if the A1 code clears after a full reset (5–10 minutes with power off).

If A1 returns and wiring is intact, the Daikin main PCB is likely defective and must be replaced. Board replacement should be performed by a qualified technician to ensure correct configuration and safe operation.