What does Mitsubishi Electric error U0 mean?

Error U0 indicates a refrigerant shortage (gas leak) or a blocked refrigerant cycle. In Canberra, this often appears when the system struggles to heat effectively. It requires a licensed technician to pressure test and repair.

Why does my Mitsubishi controller say 'Standby' or 'Defrost'?

This is NOT a fault. In Canberra winters (below 5 degrees), the outdoor unit freezes. The system pauses heating to melt this ice. Wait 10-15 minutes, and it will resume heating automatically.

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Troubleshooting Summary

Updated for 2026: If your Mitsubishi Electric system stops working, the "Operation" light will blink, or an error code (e.g., U0, P8, E6) will appear on the wired controller. This indicates a "Protective Stop".

First Step: Perform a "Hard Reset" by turning off the outdoor isolator switch for 20 minutes. If the code returns, consult the tables below.

ACT Climate Check: Is it actually broken?

Canberra winters often drop below zero. Your Mitsubishi Electric unit has built-in modes to handle this. These are NOT faults:

"Defrosting" or "Standby"

The system pauses heating to melt ice on the outdoor unit. You may see steam outside. Do not turn off. Wait 15 mins.

"Pre-Heat"

On start-up, the fan waits until the internal coil is hot before blowing air, to prevent cold draughts.

1. Wired Controller Codes (Ducted Systems)

For systems with a wall-mounted controller (e.g., PAR-31, PAR-40). The code usually appears in the top right or center of the screen.

Code	Diagnosis	Action
U0	Refrigerant Shortage. The sensor detects low gas pressure (Leak) or a blocked cycle.	Call Pro
P8	Pipe Temperature. Outdoor or indoor coil temperature is abnormal. Often sensor failure or gas issue.	Call Pro
E6 / E7	Comms Error. Indoor/Outdoor units lost connection. Common after ACT lightning storms.	Try Reset
P9	Thermal Sensor. The pipe temperature sensor isn't contacting the pipe correctly.	Call Pro
6607	No Address. The controller cannot find the unit. Circuit board failure.	Call Pro
UP	Overcurrent. Compressor stopped due to power surge or seizure.	Urgent

2. Blinking Light Patterns (Split Systems)

For wall-mounted units (MSZ Series). Count the number of blinks on the "Operation" (Green) LED.

2 Blinks Indoor Sensor

The room temperature thermistor or pipe thermistor is faulty/disconnected.

5 Blinks Outdoor Fault

General fault in the outdoor unit. Compressor, fan, or power board.

6 Blinks Indoor Fan

The internal fan motor is jammed or failed. Check for obstructions.

7 Blinks Board Failure

Indoor control board (PCB) failure or lack of refrigerant.

Error Code Persisting?

Mitsubishi Electric systems are complex ("Diamond Quality"). If a reset doesn't work, you likely have a sensor or PCB issue. We are Authorized Service Agents in Canberra.

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