Free reference

Aircon fault code lookup.

Search or filter by brand to decode what a flashing error on your split, ducted or multi-head aircon actually means. Each entry lists the likely cause and the first thing to check before booking a service call. Covers every major brand we install plus the ones we don’t.

Brand	System	Code	Likely meaning	First check
Mitsubishi Electric	Air conditioner	P1	Indoor room-thermistor fault	Indoor unit thermistor loose or failed, needs a service call.
Mitsubishi Electric	Air conditioner	P2	Indoor pipe-thermistor fault	Pipe sensor open-circuit, usually a swap-out fix.
Mitsubishi Electric	Air conditioner	P4	Drain sensor fault	Check the condensate drain pan isn't clogged; sensor may need replacing.
Mitsubishi Electric	Air conditioner	P5	Drain pump fault	Condensate pump seized or blocked, clear the drain line and re-test.
Mitsubishi Electric	Air conditioner	P6	Coil frost / overheat protection	Filter blocked or airflow restricted. Clean filters + check outdoor coil.
Mitsubishi Electric	Air conditioner	P8	Pipe temperature abnormal	Low refrigerant charge or restriction. Needs an ARC-licensed tech.
Mitsubishi Electric	Air conditioner	E0	Remote-control transmission error	Wired controller comms drop, check controller wire terminations.
Mitsubishi Electric	Air conditioner	E6	Indoor / outdoor comms failure	Check the S1-S2-S3 comms wire between indoor & outdoor units.
Mitsubishi Electric	Air conditioner	E9	Indoor / outdoor comms error (variant)	Same as E6, comms cable, check for damage or loose terminals.
Mitsubishi Electric	Air conditioner	U2	Compressor overheat / oil shortage	STOP using the unit. Compressor at risk, book a warranty service call.
Mitsubishi Electric	Air conditioner	U4	Outdoor thermistor open-circuit	Outdoor coil or discharge sensor faulty. Tech required.
Daikin	Air conditioner	A1	Indoor PCB defect	Indoor board fault, power-cycle the unit first, then service if it returns.
Daikin	Air conditioner	A5	High-pressure control / freeze-up protection	Filter dirty or outdoor coil blocked. Clean both, re-test.
Daikin	Air conditioner	A6	Indoor fan motor fault	Fan motor stalled or capacitor failed. Service call.
Daikin	Air conditioner	C4	Indoor heat-exchanger thermistor fault	Sensor open-circuit, swap-out fix.
Daikin	Air conditioner	C9	Indoor air suction thermistor fault	Room-temp sensor failed. Service call.
Daikin	Air conditioner	E1	Outdoor PCB defect	Outdoor board fault. Power-cycle first, then book service.
Daikin	Air conditioner	E5	OL activated (compressor overload)	STOP unit. Compressor overload, likely refrigerant charge or fan issue.
Daikin	Air conditioner	E6	Compressor lock / start failure	STOP unit. Compressor won't spin up. Warranty / service.
Daikin	Air conditioner	E7	Outdoor fan motor lock	Check for debris jamming the outdoor fan. If clear, motor swap.
Daikin	Air conditioner	F3	Discharge-pipe temperature too high	Low refrigerant charge or blocked outdoor coil. ARC tech needed.
Daikin	Air conditioner	L5	Inverter compressor abnormal	STOP unit. Inverter fault, warranty repair.
Daikin	Air conditioner	U0	Refrigerant shortage	Refrigerant low, check for leak, book an ARC-licensed tech.
Daikin	Air conditioner	U4	Indoor / outdoor comms error	Check the F1-F2 comms wire, loose terminal or damaged cable.
Fujitsu	Air conditioner	E:EE	Room-temp thermistor fault	Thermistor open, sensor swap.
Fujitsu	Air conditioner	E:11	Comms error indoor ↔ outdoor	Comms wire fault. Check terminals both ends.
Fujitsu	Air conditioner	E:12	Outdoor comms not responding	Outdoor board or power supply, book service.
Fujitsu	Air conditioner	E:14	Signal transmission error (wired remote)	Wired controller, check the H1-H2 line terminations.
Fujitsu	Air conditioner	OP:00	Outdoor high-pressure protection	Airflow blocked at outdoor unit. Clear obstructions and re-test.
Fujitsu	Air conditioner	OP:04	Compressor discharge-temp protection	STOP unit. Likely low charge or blocked coil.
Panasonic	Air conditioner	H11	Indoor / outdoor comms failure	Comms cable fault. Check terminals.
Panasonic	Air conditioner	H15	Compressor sensor error	Sensor failed, service call.
Panasonic	Air conditioner	H27	Outdoor air sensor error	Sensor open, swap-out fix.
Panasonic	Air conditioner	F91	Refrigerant abnormal (leak)	STOP unit. Refrigerant leak, ARC tech needed.
Panasonic	Air conditioner	F99	Outdoor DC over-current	STOP unit. Inverter / compressor fault. Warranty service.
LG	Air conditioner	CH01	Indoor room-thermistor error	Sensor open, swap fix.
LG	Air conditioner	CH02	Indoor pipe sensor error	Sensor open, swap fix.
LG	Air conditioner	CH05	Indoor / outdoor comms error	Comms cable, check terminals both ends.
LG	Air conditioner	CH21	IPM fault (inverter power module)	STOP unit. Inverter power stage, book warranty service.
Kaden	Air conditioner	E1	Indoor & outdoor comms error	Check comms cable connection between heads.
Kaden	Air conditioner	E2	Room temp sensor fault	Sensor open, sensor swap by installer.
Kaden	Air conditioner	E5	Overcurrent protection	Airflow blocked or refrigerant charge low. Service call.
Kaden	Air conditioner	F1	Outdoor unit sensor fault	Outdoor sensor swap, book service.
Kaden	Air conditioner	F3	Compressor discharge temp too high	STOP unit. Likely low charge. ARC tech required.
Brivis	Gas heater	h01 30	Fan limp mode, fan speed sensor signal invalid	Unit runs at safe speed. Book gas heater service, main fan sensor or motor.
Brivis	Gas heater	h01 31	Flame roll-out during ignition (auto restart)	Unit will attempt to restart. If it persists, book service, roll-out sensor / burner alignment.
Brivis	Gas heater	h01 32	Data error, parameters reset to default	Controller memory fault. Book service to re-commission the unit.
Brivis	Gas heater	h01 33	Modulating gas valve, open circuit on coil	Modulation coil fault. Needs a gas fitter service call.
Brivis	Gas heater	h01 35	Supply-air thermistor fault (open / short)	Sensor swap by installer, no heat until fixed.
Brivis	Gas heater	h01 36	Bad supply-air thermistor location	Thermistor not reaching setpoint in time, indicates blocked ducts or sensor moved. Book service.
Brivis	Gas heater	h01 37	Speed sensor error, unit in safe mode	Main-fan speed signal wrong. May lockout if persistent. Book service.
Brivis	Gas heater	h01 40	Return-air overheat, flue-fan overheat switch open	Return-air blockage or fan issue. Clean return-air filter first, then service.
Brivis	Gas heater	h01 41	Supply-air overheat switch tripped	Blocked supply ducts / grille. Check no vents shut. Service if it persists.
Brivis	Gas heater	h01 42	Supply-air thermistor temp exceeded overheat threshold	Duct blockage forcing overheat. Open all vents, clean filter, book service if persists.
Brivis	Gas heater	h01 43	Overheat cool-down in progress	Unit cooling itself down safely. Wait 5 min. If it recurs, service.
Brivis	Gas heater	h01 44	Flame roll-out detected during ignition	Roll-out sensor triggered. Book gas fitter, burner or heat exchanger issue.
Brivis	Gas heater	h01 45	Low 24V AC supply voltage	Power supply issue on the low-voltage transformer. Service call.
Brivis	Gas heater	h01 46	No flame on ignition attempt	Check gas isolation valve is on. If good, book a gas fitter, igniter, gas pressure, or flame rod.
Brivis	Gas heater	h01 47	Unstable flame, dropped during validation	Gas pressure or flame rod issue. Book a gas fitter.
Brivis	Gas heater	h01 48	Pressure loss, combustion chamber switch opened mid-cycle	Flue restriction or fan issue. Book service, check flue is clear.
Brivis	Gas heater	h01 49	Flame lost during heating cycle	Gas supply interruption or flame sensor issue. Book gas fitter.
Brivis	Gas heater	h01 50	Ignition lockout, max ignition attempts exceeded	STOP unit. Power cycle at the wall control to reset. If it re-locks, gas fitter required.
Brivis	Gas heater	h01 51	Roll-out signal with no gas active (sensing circuit fault)	Roll-out sensor circuit fault. Book service.
Brivis	Gas heater	h01 52	Flame signal detected with no gas, flame sensing circuit fault	Flame rod / control board fault. Book service.
Brivis	Gas heater	h01 53	Overheat lockout	STOP unit. Overheat safety triggered multiple times. Gas fitter required before use.
Brivis	Gas heater	h01 54	Roll-out lockout, max roll-out events during heat cycle	STOP unit. Repeated roll-out, burner / heat exchanger inspection required.
Brivis	Gas heater	h01 55	Flame validation lockout, flame lost repeatedly at validate step	STOP unit. Book gas fitter, flame or gas supply issue.
Brivis	Gas heater	h01 56	Pressure switch stuck open, flue fan on but no pressure	Pressure switch or tube blocked. Book service.
Brivis	Gas heater	h01 57	Pressure switch stuck closed, flue fan off but pressure detected	Pressure switch stuck. Book service.
Brivis	Gas heater	h01 58	Pressure switch fail, max pressure-loss events exceeded	STOP unit. Flue / pressure switch fault. Book service.
Brivis	Gas heater	h01 59	Cross-check comms error between primary and secondary MCU	Control board comms fault. Board-level service required.
Brivis	Gas heater	h01 60	Motor open circuit, no zero-cross detect signal	Fan motor open circuit, book service. Motor swap likely.
Brivis	Gas heater	h01 61	Primary valve stuck off, relay contact not closing	Gas valve relay fault. Book gas fitter.
Brivis	Gas heater	h01 62	Primary valve stuck on, relay contact welded	STOP unit. Gas valve relay stuck. Gas fitter needed immediately.
Brivis	Gas heater	h01 63	Primary valve fail, relay not closing during heating	STOP unit. Gas valve fault. Book gas fitter.
Brivis	Gas heater	h01 64	Modulating valve overcurrent (>150 mA)	Modulation coil short. Book service.
Brivis	Gas heater	h01 65	Motor lockout, fan limp + open circuit or overheat combo	STOP unit. Multiple fan faults combined. Book service.
Brivis	Gas heater	h01 66	Secondary valve stuck off	Second gas valve relay fault. Gas fitter.
Brivis	Gas heater	h01 67	Secondary valve stuck on	STOP unit. Gas valve stuck. Gas fitter needed immediately.
Brivis	Gas heater	h01 68	Secondary valve fail during heating	STOP unit. Gas fitter required.
Brivis	Gas heater	h01 69	Fuse blown, 24V AC voltage lost	2A fuse on the control board is open. Service call to replace + diagnose why it blew.
Brivis	Gas heater	h01 70	Remote MCU shutdown fail	Control-board fault. Board-level service.
Brivis	Gas heater	h01 71	Remote MCU state mismatch	Control-board fault. Board-level service.
Brivis	Gas heater	h01 72	Ambiguous fault, unattributed shutdown	Undiagnosed shutdown. Book service to read secondary log.
Brivis	Gas heater	h01 73	Remote MCU next-state mismatch	Control-board firmware or hardware fault. Book service.
Brivis	Gas heater	h01 74	Remote MCU lockout (secondary board locked)	STOP unit. Board-level service required.
Brivis	Gas heater	h01 75	AC input scan fault, 24V input stuck high	Input scanning circuit fault. Board-level service.
Brivis	Gas heater	h01 76	Lockout storage fault, non-volatile memory access failure	Control board's ability to store lockouts compromised. Book service.
Brivis	Gas heater	h01 77	Remote MCU IO mismatch	IO state mismatch between board MCUs. Book service.
Brivis	Gas heater	h01 79	A/D converter reference voltage check failed	Board-level analog fault. Service.
Brivis	Gas heater	h01 80	Flame sense fault, measured voltage out of range	Flame rod or sensing circuit fault. Book gas fitter.
Brivis	Gas heater	h01 81	Roll-out sense fault, sensor voltage out of range	Roll-out sensor circuit fault. Book service.
Brivis	Gas heater	h01 82	System timing fault, MCU timing vs 50 Hz mismatch	Control-board timing fault. Board-level service.
Brivis	Gas heater	h01 83	System execution fault, internal MCU error	Control-board firmware fault. Board-level service.
Brivis	Gas heater	h01 84	Control board lockout (system lockout initiated)	STOP unit. Board-level service required.
Brivis	Gas heater	h01 85	Control board lockout (system lockout initiated)	STOP unit. Board-level service required.
Brivis	Gas heater	h01 86	Control board lockout (system lockout initiated)	STOP unit. Board-level service required.
Brivis	Gas heater	h01 87	Cross-check comms fault, no MCU comms >10 s	Control-board comms failure. Board-level service.
Brivis	Gas heater	h01 88	Control board lockout (system lockout initiated)	STOP unit. Board-level service required.
Brivis	Gas heater	h01 89	MCU non-volatile storage test code (not seen in normal use)	Diagnostic-only code, service tech will interpret. If it appears on normal operation, book service.
Reclaim	Hot water	E1	Ambient temp sensor fault	Outdoor sensor open-circuit. Book a Reclaim-accredited service tech.
Reclaim	Hot water	E2	Evaporator temp sensor fault	Evaporator sensor fault, swap-out fix by a tech.
Reclaim	Hot water	E3	Discharge / suction sensor fault	Sensor swap by an ARC-licensed tech.
Reclaim	Hot water	E4	Tank temp sensor fault	Tank thermistor open, sensor swap. Water still heats via boost.
Reclaim	Hot water	E5	High-pressure fault (CO2)	STOP unit. Refrigerant charge / heat-exchanger issue. Warranty service.
Reclaim	Hot water	E6	Low-pressure fault (CO2)	STOP unit. Likely refrigerant leak, Reclaim tech required.
Reclaim	Hot water	E7	Compressor overload	STOP unit. Compressor at risk, book warranty service.
Reclaim	Hot water	F1	Comms error tank ↔ heat pump	Check the comms wire between the outdoor heat pump and the tank controller.
iStore	Hot water	E1	Ambient temp sensor fault	Sensor open-circuit. Book service, water will still heat on boost element.
iStore	Hot water	E2	Evaporator sensor fault	Sensor swap by installer.
iStore	Hot water	E3	Condenser sensor fault	Sensor open, service call.
iStore	Hot water	E4	Tank sensor fault	Tank thermistor fault, sensor swap.
iStore	Hot water	E5	Compressor high pressure	STOP unit. Likely blocked evaporator airflow. Clean coil.
iStore	Hot water	E7	Anti-freeze protection triggered	Very cold ambient, normal in winter. If persistent, book service.
iStore	Hot water	E8	Compressor drive fault	STOP unit. Inverter drive fault, warranty repair.
Thermann	Hot water	E1	Water temp sensor fault (integrated HP)	Sensor open, Thermann service call.
Thermann	Hot water	E2	Ambient sensor fault	Sensor open, swap by installer.
Thermann	Hot water	E5	Compressor overload	STOP unit. Book warranty service.
Thermann	Hot water	F1	Comms error (integrated HP)	Check internal comms wire between board and controller.
Thermann	Hot water	12	G-series continuous flow, ignition failure	Check gas supply on. If OK, needs a licensed gas fitter.
Thermann	Hot water	11	G-series, no ignition detected	Gas valve or igniter fault. Book a gas fitter.
Braemar	Gas heater	23	Overheat lockout	Blocked filter or return-air path. Clean filter and reset.
Braemar	Gas heater	27	Ignition failure (no flame sensed)	Check gas is on. If OK, needs a licensed gas fitter to inspect igniter + flame sensor.
Braemar	Gas heater	42	Fan proving switch fault	Fan not detected running. Book gas heater service.
Braemar	Gas heater	51	Wall-controller comms lost	Check the low-voltage comms wire between controller and unit.
Braemar	Gas heater	58	Zone motor / damper fault	One zone motor stuck, book service to swap the damper motor.
Bonaire	Evap cooler	E01	Water pump fault (evap)	Check evap water supply on. If OK, pump swap needed.
Bonaire	Evap cooler	E02	Water level fault (evap)	Water inlet blocked or float stuck. Clean the reservoir.
Bonaire	Evap cooler	E04	Fan motor fault	Motor seized or capacitor gone. Book service.
Bonaire	Evap cooler	E05	Ambient temp sensor fault	Outdoor sensor open, sensor swap by installer.
Bonaire	Evap cooler	E12	Comms error (integrated system)	Check comms wire between wall controller and unit.
Sanden	Hot water	F1	Comms error tank ↔ heat pump	Check the comms cable between heat pump and tank controller.
Sanden	Hot water	F2	Tank temp sensor fault	Tank thermistor swap, service call.
Sanden	Hot water	F3	Ambient sensor fault	Outdoor sensor open. Service call.
Sanden	Hot water	F5	High-pressure protection (CO₂)	STOP unit. Refrigerant issue. Warranty tech required.
Sanden	Hot water	F7	Compressor overload	STOP unit. Book warranty service.
Rheem	Hot water	1	Water temp sensor fault	Sensor open, book service. Element still heats but at fixed temp.
Rheem	Hot water	12	Ignition failure (gas storage)	Check gas supply. If OK, needs a gas fitter, igniter or valve fault.
Rheem	Hot water	14	Blocked flue	STOP unit. Flue restriction / no draft. Gas fitter required immediately.
Rinnai	Hot water	11	No ignition on gas continuous flow	Check the gas isolation valve is open. If OK, gas fitter needed.
Rinnai	Hot water	12	Flame failure (drops out mid-shower)	Gas pressure low or igniter dirty. Book Rinnai service.
Rinnai	Hot water	14	Thermal fuse activated (overtemp)	STOP unit. Overheat safety triggered, book service before use.
Rinnai	Hot water	16	High temp warning	Temperature setting or thermistor issue. Check controller setpoint first.
Rinnai	Hot water	61	Fan motor fault	Fan not spinning. Book service.
Mitsubishi Electric	Air conditioner	P7	System error / multi-head miswire	Indoor unit address conflict on multi-head. Requires MXZ config check.
Mitsubishi Electric	Air conditioner	U8	Outdoor DC voltage abnormal	STOP unit. Power supply or inverter drive fault, warranty service.
Daikin	Air conditioner	H9	Outdoor ambient sensor fault	Sensor open, swap fix.
Daikin	Air conditioner	J3	Discharge pipe thermistor fault	Sensor swap by installer.
Daikin	Air conditioner	P4	Heat sink temperature abnormal	STOP unit. Inverter overheat. Warranty service.

Showing 149 of 149 codes

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Past about ten years on hot water and gas heating, and twelve on aircon, a significant repair usually costs more per remaining year than a replacement does — and it’s the same point at which the VEU rebate is worth the most. If yours is young and the fault is a component, we’ll fix it and say so.

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