Daikin furnace intermittently shuts down with U2 error; blower may run but no heat, or unit locks out after several attempts.

Safety: Turn off power at the furnace disconnect or breaker before removing any panels. Use a multimeter only if you are familiar with electrical safety.

Steps to check:

• Inspect power connections: Remove the blower door and locate the Daikin main control board. Check that all line voltage wires (L1, L2/neutral) are firmly seated and not discolored or burnt.
• Check breaker and wiring: At the electrical panel, verify the furnace breaker is fully ON and not warm or buzzing. Ensure the furnace is on a dedicated circuit where possible.
• Measure voltage (qualified persons only): With power on, measure voltage at the furnace line terminals. It should be within the range specified on the furnace nameplate (typically around 120 VAC). Significant deviation indicates a supply issue.
• Inspect low-voltage transformer: Locate the 120V–24V transformer on or near the Daikin control board. Check for signs of overheating, humming, or oil leakage. Loose low-voltage connections (R, C) can also cause intermittent U2 errors.
• Reduce shared loads: If the furnace shares a circuit with large appliances, move those loads to another circuit to reduce voltage drop.

If U2 persists after confirming proper voltage and tight connections, a technician should test the transformer and Daikin control board under load and replace the faulty component.