Mitsubishi Electric mini split error code U5
Inverter heat sink temperature abnormal.
- TypeProtection
- SystemCompressor / inverter
- Can I fix it?Homeowner checks, then maybe a tech
What U5 means on a Mitsubishi Electric
The inverter's heat sink got too hot and the compressor stopped.
On this platform, U5 is a protection: the system stopped or throttled itself to prevent damage; many clear on their own once conditions return to normal.
Common causes
- A blocked outdoor coil or failed fan.
- Blocked clearance around the outdoor unit.
- A failed heat-sink thermistor.
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.
- Look at the outdoor unit: clear leaves, cottonwood fluff, snow or ice from the coil and make sure the fan can spin freely and nothing is stacked against the cabinet.
- Check clearance around the outdoor unit.
- 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.
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
Persistent U5 with a clean coil needs a technician.
Which Mitsubishi Electric units show U5
This page applies to Mitsubishi Electric M-Series (MSZ), Mr. Slim (PKA/PCA), Hyper-Heating H2i and MXZ multi-zone units. Mitsubishi Electric's own documentation lists U5 as "Inverter heat sink temperature abnormal", the same definition used across the Mitsubishi Electric 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 Mitsubishi Electric shows this code
Wall units without a wired controller signal a fault by blinking the operation indicator lamp; the code itself shows on a wired controller (MHK/PAR series) or on the wireless remote after entering its check mode (see your manual). On the outdoor unit, the control board LEDs blink the same code. P codes are indoor-unit faults, E codes are communication faults, F codes are outdoor-unit faults and U codes are outdoor-unit and compressor faults.
Other Mitsubishi Electric codes
Same part of the system as U5:
U5 on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Blueridge U5 Whole-unit current detection error
- Daikin U5 Communication error between indoor unit and remote controller
- Trane U5 Inverter heat sink temperature abnormal
Questions people ask
Can I reset a Mitsubishi Electric 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 Mitsubishi Electric showing U5?
Not repeatedly. A protection code means the unit stopped itself to prevent damage, and resetting it over and over can turn a cheap repair into a compressor failure. Reset once, check the basics, and stop if it returns.
Do I need a technician for Mitsubishi Electric U5?
Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician. Persistent U5 with a clean coil needs a technician.
Sources
- Mitsubishi Electric M-Series and Mr. Slim service manuals (self-diagnosis tables)
Updated September 2026. Codes and definitions vary by model year. If your manual disagrees with this page, your manual wins. Send a correction.