DIY HVAC Tools

Daikin mini split error code U5

Communication error between indoor unit and remote controller.

  • TypeFault
  • SystemCommunication
  • Can I fix it?Homeowner checks, then maybe a tech

What U5 means on a Daikin

A wired remote controller and the indoor unit stopped talking.

On this platform, U5 is a fault: something has failed or is disconnected and needs diagnosis.

Common causes

  • A loose or damaged controller cable.
  • A failed controller or indoor board.
  • Two controllers both set as main.

How to fix it yourself

Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician.

  1. Reset the system: switch the breaker (or the outdoor disconnect) off, wait a full five minutes so the boards fully discharge, then switch it back on and restart from the remote.
  2. With power off, reseat the controller cable at both ends.

Switch off power at the breaker before opening either unit. Capacitors in the outdoor unit hold a charge for several minutes after power is cut.

When to call a technician

A technician can test the controller and board.

Which Daikin units show U5

This page applies to Daikin Aurora, 19 Series, Atmosphera, Emura, Quaternity and MXS multi-zone units. Daikin's own documentation lists U5 as "Communication error between indoor unit and remote controller", the same definition used across the Daikin it is built on. If your unit shows a code with a different shape (for example a four-character code, or a plain number), it is from a different table; use the lookup with your exact code.

Where Daikin shows this code

Most Daikin wall units do not show the code on the unit; the operation lamp blinks. To read the code, point the remote at the unit, hold CANCEL (or Timer Cancel) for about 5 seconds until 00 shows, then press CANCEL repeatedly. Each press shows a code; when the unit gives a long continuous beep instead of two short beeps, the code on the remote is the stored fault. Units with a wired controller show the code directly. A and C codes are indoor-unit faults, E, F, H, J, L and P codes are outdoor-unit faults and protections, and U codes are system-level problems such as communication, power supply and refrigerant shortage.

Other Daikin codes

Same part of the system as U5:

LCCommunication error between outdoor control and inverter boardsU4Communication error between indoor and outdoor units
00No fault stored (normal)A1Indoor unit control board (PCB) failureA3Drain water level abnormal (float switch)A5Freeze-up protection (cooling) or high-pressure control (heating)A6Indoor fan motor fault (locked or abnormal)A9Indoor electronic expansion valve (EEV) faultC4Indoor heat exchanger (liquid pipe) temperature sensor fault (open or short circuit)C5Indoor heat exchanger (gas pipe) temperature sensor fault (open or short circuit)

All Daikin error codes

U5 on other brands

The same characters do not always mean the same thing. Check the brand on your unit.

Questions people ask

Can I reset a Daikin U5 code myself?

Yes. Turn the system off at the breaker for five minutes, then restart it. If U5 comes back, the fault is real and needs the checks above.

Is it safe to keep running a Daikin showing U5?

The unit will usually refuse to run, or run with reduced output, until the fault is cleared. Repeated resets do not fix anything and can mask a problem that is getting worse.

Do I need a technician for Daikin U5?

Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician. A technician can test the controller and board.

Sources

  • Daikin residential (RA) service manuals (error code tables)
  • Daikin operation manuals (remote controller self-diagnosis)

Updated September 2026. Codes and definitions vary by model year. If your manual disagrees with this page, your manual wins. Send a correction.