Heat Pump Error Code Lookup

Type the code your system is showing. Every entry below comes from our own brand guides, each of which is reviewed before publication. If a code is not in here, the tool says so rather than guessing — a wrong code sends you to the wrong repair.

Every code in the tool

The same 26 entries the lookup above searches, listed in full so you can scan them. Each links to the brand guide it came from.

Brand	Code	What it points to	What to do
Mitsubishi	P1	Indoor intake thermistor damaged or disconnected	Technician. The sensor itself is an inexpensive part.
Mitsubishi	P6	Freeze or overheat protection tripped, often from a dirty filter, dusty blower wheel or blocked airflow	Clean the filter and check airflow before calling.
Mitsubishi	E6	Indoor-to-outdoor communication error, usually the interconnecting cable or a control board	Look for obvious wiring damage, then call.
Mitsubishi	E9	Outdoor air sensor malfunction or disconnection	Technician.
Mitsubishi	U2	Power supply abnormality	Technician only. Do not repeatedly power cycle.
Daikin	A3	Drain level control fault	Clogged drain, drain line sloping the wrong way, failed drain pump or a stuck float switch.
Daikin	A5	Indoor coil freezing or overheating	Dirty filter, restricted airflow or a faulty coil sensor.
Daikin	A6	Indoor fan motor fault	Motor locked, overloaded, or a bad connection.
Daikin	C4 / C9	Indoor thermistor resistance abnormal	Disconnected or short-circuited sensor wire.
Daikin	E3	High pressure too high	Blocked or dirty outdoor coil, restricted airflow, or overcharge.
Daikin	E4	Low pressure too low	Low refrigerant, a restriction in the piping, or a faulty pressure switch.
Daikin	E7	Outdoor fan not working	Obstruction, failed fan motor, or control board fault.
Daikin	F3	Discharge temperature too high	Low charge, restricted piping, or a faulty discharge thermistor.
Daikin	H6	Position detection sensor fault	Compressor problem, outdoor board, or poor contacts.
Daikin	L5	Inverter overloaded	Failing compressor or inverter board.
Daikin	U0	Suction pipe temperature too high	Low refrigerant, a restriction, or an expansion valve fault.
Daikin	U2	Power voltage problem	Open phase, voltage imbalance or a supply fault.
Daikin	U4	Indoor to outdoor communication failure	Damaged communication wire, loose terminal, or a failed board.
Daikin	UA	Unit combination or setup error	Wrong indoor and outdoor pairing, or an incorrect field setting.
LG	CH01	Indoor air temperature sensor fault	Open or shorted sensor circuit, or a disconnected sensor plug.
LG	CH05	Communication failure between indoor and outdoor units	Loose or damaged communication wire, terminal corrosion, or board damage after a surge.
LG	CH10	Discharge temperature exceeded its limit	Usually a faulty discharge thermistor, but can indicate a genuine refrigerant problem.
LG	CH38	Low refrigerant pressure	Refrigerant leak. Needs an EPA 608 certified technician.
Fujitsu	11	Serial communication error between indoor and outdoor units	Wiring disconnect, failed indoor or outdoor PCB, or a branch box fault on multi-zone systems.
Fujitsu	53	Drainage error	Failed drain pump or a plugged drain line.
Fujitsu	97	Outdoor fan motor error	Debris around the fan, a shorted or broken motor wire, a failed motor, or a failed outdoor PCB.

Carrier publishes fault information by category rather than as a fixed code list, so its guide covers the families instead. Mitsubishi and Daikin also group codes by first character, which the tool uses to narrow a code it does not carry.

How to find the code in the first place

Where the code appears depends on what you own. Ducted systems with a wall control usually show it on the thermostat screen. Mini splits often have no display at all and report the fault as a blink pattern on the indoor unit, which you have to count.

• Wall controller or thermostat: the code appears on screen, sometimes only after you enter a service menu.
• Indoor unit LEDs: count the flashes. On Fujitsu, OPERATION blinks give the first digit and TIMER blinks the second.
• Outdoor control board: a seven-segment display or an LED sequence, visible only with the service panel off. Kill the power at the disconnect first.

What a code does not tell you

A fault code names the symptom the control board detected, not the part that failed. A communication error is usually wiring rather than a board. A high-pressure trip is usually a blocked coil rather than a compressor. Treat the code as the start of the diagnosis, not the end of it.

Two rules worth keeping regardless of what the code says: do not repeatedly reset a system that keeps faulting, and do not keep resetting a breaker that trips. Both turn a repair into a replacement.

Common questions

My code is not in the list. What now? The tool only carries codes we have written up and checked, so gaps are expected rather than a fault. Go to your brand's guide below for the code families, which will tell you which subsystem the code belongs to, then to the manufacturer's own service literature for the exact meaning.

Can I clear a code by cutting the power? It usually clears the display, and if the underlying condition is gone the system runs normally again. If the condition is still there the code returns, often within minutes. A code that returns immediately after a reset is telling you something real.

Does the same code mean the same thing on every model? No, and this is where published charts disagree with each other. Code meanings vary by series and by year within a brand. Confirm against the service literature for your specific model before buying a part.

How this guide is put together

Diagnostic steps here are ordered by how often each cause turns out to be the answer, not by how serious it is. That is deliberate: working the common causes first is what saves you a service call, and the rare-but-severe ones are flagged where they apply.

• Sources. Manufacturer installation and service manuals, published fault-code tables, and the documentation linked at the foot of this page.
• The DIY line. Anything involving refrigerant is legally restricted to an EPA Section 608 certified technician. Sealed systems, capacitors and line-voltage wiring are called out as technician work rather than left ambiguous.
• Where brands differ. Code meanings and defrost behaviour vary by series and model year. Where published charts disagree with each other, we say so instead of picking one.

Sources

Primary references for the figures and procedures on this page. Where a number here is a range drawn from field experience rather than a published measurement, it is labelled as such in the text.

• EPA Section 608 Technician Certification — Who is legally permitted to handle refrigerant, and why.
• ENERGY STAR: Air-Source Heat Pumps — Current federal efficiency criteria and the qualifying product list.
• AHRI Directory of Certified Product Performance — Look up a specific model’s certified capacity and efficiency ratings.

Last checked September 2026. Code meanings vary by series and model year; always confirm against your unit's service literature before buying parts.