Daikin: Indoor/Outdoor Communication Error
What this fault means
The heat pump lost the data link between the indoor and outdoor units and stopped — Daikin reports this in the U-series (e.g. U4) on the indoor display or remote.
Likely causes
- Damaged or loose interconnect wiring
- Corroded outdoor terminal block (coastal BC)
- Failed indoor or outdoor PCB
- Incorrect wiring after a past service
What you can safely check
- Replace a dirty air filter — restricted airflow causes a surprising share of furnace faults.
- Confirm registers and the outdoor unit are clear of snow, leaves and debris.
- Cycle power at the switch once and let the system retry.
Call a technician — don't keep resetting this
Indoor/Outdoor Communication Error is a high-severity fault. Repeated resets of a safety lockout can mask a serious problem such as a cracked heat exchanger (a carbon-monoxide risk) or a failing compressor. If you smell gas, leave and call FortisBC at 1-800-663-9911 or 911 first.
Related Daikin faults
Daikin heat pump showing Indoor/Outdoor Communication Error?
CANRO Heating & Cooling — same-day diagnosis across Greater Vancouver. Call 604-359-1081.