What causes Mitsubishi Mini Split P8?

A pipe thermistor (liquid pipe TH2 or condenser/evaporator TH5) that has come loose from its holder on the pipe, so it reads air instead of the coil. Mitsubishi's Mr. Slim error chart puts this check first. A shortage of refrigerant, so the coil doesn't get cold (or hot) enough. A stop (service) valve on the outdoor unit that isn't fully opened, which often shows up right after a new installation. On systems with more than one indoor unit, crossed (converse) extension piping, or indoor/outdoor connecting wires landed on the wrong unit, so each indoor unit watches the wrong circuit. A faulty room (intake) or pipe thermistor that reads the wrong temperature. A defective refrigerant circuit.

How do I fix Mitsubishi Mini Split P8?

Note whether P8 appeared while cooling or heating and how long the unit had been running. Mitsubishi's detection takes at least 9 minutes in cooling and 27 minutes in heating, which helps a technician. Check that the indoor unit's air filters are clean and the air intake and outlet aren't blocked, so the coil temperature can change normally. If the system was installed or worked on recently, call the installer back first. Mitsubishi's checks for P8 include a stop valve left closed and crossed piping or wiring on multi-unit systems, both installation items. If you have more than one indoor unit and only one shows P8, tell the technician which one. That is the pattern crossed piping or wiring tends to produce. Turn the system off at the breaker for a few minutes, then restart it and run it in cooling or heating long enough to see whether P8 comes back. If it returns, call a licensed HVAC technician. The remaining checks involve sensors inside the indoor unit, valves on the outdoor unit and refrigerant pressures.

When should I call a pro for Mitsubishi Mini Split P8?

The technician checks that the TH2 and TH5 pipe thermistors are seated in their holders on the indoor coil, then measures their resistance, as Mitsubishi's chart directs. On a recent install, the outdoor stop valves are checked to make sure they are fully open. On multi-unit systems, the extension piping and indoor/outdoor connecting wires are traced to make sure each indoor unit is on its own circuit. Mitsubishi's manual has the technician compare pipe and room temperature readings on the remote controller and the outdoor board (via SW2 or the A-Control Service Tool PAC-SK52ST). A refrigerant shortage means a leak search and repair, then a correct charge, which only a licensed technician can do. The system is under warranty. Contact the installing contractor or a Mitsubishi Electric Diamond Contractor.

Code: P8🔧 Mitsubishi Mini Split

Mitsubishi Mini Split Error Code P8: Pipe Temperature Error (Meaning, Causes, Fixes)

Q: What does Mitsubishi Mini Split P8 mean?

P8 on a Mitsubishi Electric indoor unit is a pipe temperature error. The indoor unit watched its coil (pipe) temperature after the compressor started and it never moved far enough away from room temperature, so the unit decided it isn't really cooling or heating. Mitsubishi's service manual lists a pipe thermistor that has slipped out of its holder, a refrigerant shortage, a stop valve left partly closed (common right after installation), crossed piping or wiring on multi-unit systems, and a faulty thermistor or refrigerant circuit. Mitsubishi Electric's PLA-A BA4 ceiling cassette service manual (OCH482) lists P8 as "Pipe temperature error", shown as 8 blinks or beeps on the wireless remote's self-check. In cooling mode the unit judges it abnormal when the pipe temperature is not in the cooling range 3 minutes after the compressor starts and stays out of range for 6 minutes. The cooling range is the lower of the liquid pipe (TH2) and condenser/evaporator (TH5) temperatures being at least 3 C (5.4 F) below the intake air temperature (TH1), and it takes at least 9 minutes to detect. P8 is not detected in drying mode. In heating mode, once 10 seconds have passed after the compressor starts and the hot adjustment mode has finished, it is abnormal if the condenser/evaporator pipe temperature does not reach the heating range (at least 3 C, 5.4 F, above intake air) within 20 minutes. That takes at least 27 minutes to detect, and defrost time doesn't count. Neighboring codes: P2 and P9 are pipe sensor (thermistor) errors, P6 is freezing or overheating protection, and PL is a refrigerant circuit abnormality.

Reviewed 2026-10-24 · Based on 2 manufacturer & service sources

What the code means

Mitsubishi Electric's PLA-A BA4 ceiling cassette service manual (OCH482) lists P8 as "Pipe temperature error", shown as 8 blinks or beeps on the wireless remote's self-check. In cooling mode the unit judges it abnormal when the pipe temperature is not in the cooling range 3 minutes after the compressor starts and stays out of range for 6 minutes. The cooling range is the lower of the liquid pipe (TH2) and condenser/evaporator (TH5) temperatures being at least 3 C (5.4 F) below the intake air temperature (TH1), and it takes at least 9 minutes to detect. P8 is not detected in drying mode. In heating mode, once 10 seconds have passed after the compressor starts and the hot adjustment mode has finished, it is abnormal if the condenser/evaporator pipe temperature does not reach the heating range (at least 3 C, 5.4 F, above intake air) within 20 minutes. That takes at least 27 minutes to detect, and defrost time doesn't count. Neighboring codes: P2 and P9 are pipe sensor (thermistor) errors, P6 is freezing or overheating protection, and PL is a refrigerant circuit abnormality.

Likely causes

A pipe thermistor (liquid pipe TH2 or condenser/evaporator TH5) that has come loose from its holder on the pipe, so it reads air instead of the coil. Mitsubishi's Mr. Slim error chart puts this check first.
A shortage of refrigerant, so the coil doesn't get cold (or hot) enough.
A stop (service) valve on the outdoor unit that isn't fully opened, which often shows up right after a new installation.
On systems with more than one indoor unit, crossed (converse) extension piping, or indoor/outdoor connecting wires landed on the wrong unit, so each indoor unit watches the wrong circuit.
A faulty room (intake) or pipe thermistor that reads the wrong temperature.
A defective refrigerant circuit.

Safe DIY checks

⚠ Before you start

Turn off the breaker for both the indoor and outdoor units before opening any panel. Thermistors sit next to line-voltage boards inside the indoor unit, and stop valves and refrigerant lines are under pressure, so leave anything beyond filters and airflow to a licensed HVAC technician.

Note whether P8 appeared while cooling or heating and how long the unit had been running. Mitsubishi's detection takes at least 9 minutes in cooling and 27 minutes in heating, which helps a technician.
Check that the indoor unit's air filters are clean and the air intake and outlet aren't blocked, so the coil temperature can change normally.
If the system was installed or worked on recently, call the installer back first. Mitsubishi's checks for P8 include a stop valve left closed and crossed piping or wiring on multi-unit systems, both installation items.
If you have more than one indoor unit and only one shows P8, tell the technician which one. That is the pattern crossed piping or wiring tends to produce.
Turn the system off at the breaker for a few minutes, then restart it and run it in cooling or heating long enough to see whether P8 comes back.
If it returns, call a licensed HVAC technician. The remaining checks involve sensors inside the indoor unit, valves on the outdoor unit and refrigerant pressures.

🛠 When to call a pro

The technician checks that the TH2 and TH5 pipe thermistors are seated in their holders on the indoor coil, then measures their resistance, as Mitsubishi's chart directs.
On a recent install, the outdoor stop valves are checked to make sure they are fully open.
On multi-unit systems, the extension piping and indoor/outdoor connecting wires are traced to make sure each indoor unit is on its own circuit.
Mitsubishi's manual has the technician compare pipe and room temperature readings on the remote controller and the outdoor board (via SW2 or the A-Control Service Tool PAC-SK52ST).
A refrigerant shortage means a leak search and repair, then a correct charge, which only a licensed technician can do.
The system is under warranty. Contact the installing contractor or a Mitsubishi Electric Diamond Contractor.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Mini split pipe thermistor (exact part for your indoor model)

A loose or failed TH2/TH5 pipe thermistor is one of Mitsubishi's listed causes; match the part number to your model.

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⚙

Refrigerant leak detector

Refrigerant shortage is a listed cause; a technician uses one to find the leak before recharging.

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⚙

Digital multimeter

Used to check thermistor resistance against the service manual's table.

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Sources

Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.

Mitsubishi Mini Split Error Code P8: Pipe Temperature Error (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Mini split pipe thermistor (exact part for your indoor model)

Refrigerant leak detector

Digital multimeter

Related codes

Sources