Mitsubishi Mini Split Error Codes: E6, P8, P5 and What They Mean

Mitsubishi mini-split and heat pump systems flag a fault with a letter-and-number error code — shown by the blinking operation LED on the indoor unit, on the wireless remote’s check display, or directly on a wired controller. The first letter groups the problem: E codes are communication faults (between the remote and the unit, or between the indoor and outdoor units), P codes are protection trips (temperature sensors, the drain system, and freeze/overheat protection), and U and F codes point to the outdoor unit, compressor, and refrigerant circuit. Use the quick-answer table above to find your exact Mitsubishi error code, what it means, and the safe first step. Many E and P codes clear after a power cycle or a simple fix like cleaning the filter or clearing the drain; U-series codes usually need a licensed technician. Always confirm the code against your model’s Mitsubishi manual, since meanings vary by series (and VRF systems use 4-digit codes).

How to read a Mitsubishi error code

Where the code appears depends on your controller:

• Wall-mounted (M-Series) units: the operation indicator LED blinks a pattern, and the code shows on the wireless remote’s check display.
• Wired controllers (e.g. PAR series): the code shows directly on the screen.

What the first letter tells you

What to do first

For communication (E) and many protection (P) codes, start simple:

1. Turn the unit off with the remote.
2. Switch off the circuit breaker for about one minute.
3. Restore power and let the unit restart.
4. If it’s a P4/P5 (drain) code, clear the condensate drain line; if P6/P8, clean the filter and clear anything blocking airflow.

If the same code returns, stop and have it diagnosed — repeating codes, especially U-series (compressor/refrigerant), are not DIY fixes.

The codes people look up most, step by step

Mitsubishi P8

P8 is a pipe temperature protection. The control board expects the indoor coil to change temperature once the system runs; when it doesn’t, that almost always means heat isn’t being moved — either because there’s too little refrigerant, the air isn’t flowing across the coil, the outdoor unit isn’t contributing, or the sensor reading the pipe is wrong. Fixing the underlying heat-transfer problem is what clears it.

Common causes

• Low refrigerant / leak — the most common serious cause; the coil can’t reach temperature. See why a mini split isn’t cooling for related symptoms.
• Dirty filter or blocked airflow — restricts air across the indoor coil.
• Outdoor unit not running — no refrigerant cycle; check the outdoor unit.
• Faulty pipe thermistor — sensor open, shorted, or not seated against the pipe.
• Fan motor or electronic expansion valve (LEV) fault.

How to fix it

1. Clean the indoor filters and make sure the coil and vents are clear.
2. Check the outdoor unit is powered, running, and not blocked by debris.
3. Power-cycle once — off at the breaker for ~5 minutes, then restart.
4. If P8 returns, stop resetting and call a technician — it’s likely refrigerant, the pipe sensor, or the expansion valve.

Mitsubishi E6

A Mitsubishi mini split continuously sends data between the indoor and outdoor control boards over the connecting cable (terminals S1 / S2 / S3). When that signal is interrupted or unreadable, the system reports E6 and usually stops heating or cooling until communication is restored.

Common causes

• Connecting wiring fault — loose, corroded, miswired, or damaged S1/S2/S3 wires (the most common cause, especially after an install or repair).
• Power-sequencing issue — the outdoor unit energizing before the indoor unit.
• No power to the outdoor unit — a tripped breaker or off disconnect.
• Control board (PCB) fault — a defective transmit/receive circuit.
• Signal interference / noise — sometimes from a drain pump wired into S1/S2.

How to fix it

1. Power-cycle the whole system — off at the breaker for ~5 minutes, then restore power so both units start together.
2. Confirm outdoor power — breaker on, disconnect on. A dead outdoor unit looks like a communication loss; see outdoor unit not running.
3. If E6 returns, stop resetting and have a technician inspect the S1/S2/S3 connecting wiring and the control boards.

Mitsubishi P5

Every time your mini split cools, it wrings moisture out of the air. That water drips into a drain pan, and a small drain pump lifts it out to the drain line. When the unit senses the pan isn’t emptying — the float switch stays up — it throws P5 and stops, rather than letting water spill onto your floor or the electronics.

Common causes

• A clogged drain line — by far the most common. Algae and dust block the line, the pan fills, and the pump can’t keep up. (Full walkthrough: how to clear a clogged drain line.)
• A failed drain pump — the pump motor has worn out and no longer runs.
• Wiring or connector trouble at the pump — an intermittent P5 is often this.
• A stuck float switch — slime in the pan can jam the float in the “full” position.

How to fix it

1. Turn the unit off.
2. Clear the drain line. A wet/dry vacuum sealed to the outdoor end of the drain usually sucks the clog straight out. See the full drain-line clearing guide.
3. Clean the drain pan — soak up the water and wipe away slime so the float moves freely.
4. Power-cycle and listen. Restart and check that the pump hums when the unit runs. If it’s silent — or P5 returns with a clear line — the pump needs a pro.

If water is also dripping from the indoor unit, our guide to a leaking mini split covers the related symptoms.

Trademark note: “Mitsubishi Electric” and “Mr. Slim” are trademarks of Mitsubishi Electric Corporation. This page is an independent homeowner resource and is not affiliated with, authorized by, or endorsed by Mitsubishi Electric. Brand and code references are used factually for identification and troubleshooting only.