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Mitsubishi Electric Air Conditioner Fb Error Code
Indoor control board error. Here is what it means and how to clear it, easiest fix first.
The indoor unit's control board has found a fault in its own system, such as a memory read error.
These check codes appear on wired wall controllers, mainly with P-series, Mr. Slim and ducted or ceiling units; wall-mounted M-series units (MSZ) usually report faults by blinking the OPERATION light instead. The meanings here come from Mitsubishi Electric's Mr. Slim code list for Singapore models and its North American wired-controller manual, and they can differ by series and region, so check your manual.
How to fix Mitsubishi Electric Fb
Reset the power at the breaker
Switch off the breaker that feeds the air conditioner (some systems have separate breakers for the indoor and outdoor units, so switch off both). Wait about five minutes, switch the power back on and restart the unit to see if the code clears.
Note the code and when it appears
If Fb returns, write down the code, the model number from the indoor unit's label and whether it showed up at start-up or after a power cut. A control board is model-specific, so this helps the technician bring the right one.
When to call a technician
If Fb returns after a reset, the indoor control board likely needs replacing by a technician.
Parts that commonly cause Fb
- indoor control PCB
Order parts by your exact model number so they fit.
Other Mitsubishi Electric air conditioner codes
- Blinking OPERATION lightWall unit's indicator light is flashing
- P1Room air temperature sensor fault
- P2 / P9Indoor coil temperature sensor fault
- P4 / P5Drain sensor or drain pump problem
- PAShut down to prevent a water leak
- P6Freeze or overheat protection
- P8Pipe temperature error
- PbIndoor fan motor error
- E0-E5Wall controller communication error
- E6 / E7 / E9Indoor and outdoor units aren't communicating
- U1 / UdHigh pressure or overheat protection
- U2Discharge temperature too high or low refrigerant
- U3 / U4Outdoor temperature sensor fault
- U6 / UP / UFCompressor overcurrent
- U8Outdoor fan stopped
- U9 / UHPower supply or current sensor problem
- PLRefrigerant circuit abnormal
Frequently asked questions
What does Fb mean on a Mitsubishi Electric air conditioner?
The indoor unit's control board has found a fault in its own system, such as a memory read error.
Can I fix Mitsubishi Electric Fb myself?
Only the basic checks. You can safely try the steps above, but Fb usually points to a part or fault that needs a technician.
What if Fb keeps coming back?
A code that returns after a reset and the checks above usually means a part is wearing out. Note when Fb appears (which cycle, how often) and have your model number ready; it helps a technician bring the right part on the first visit.
Last reviewed 2026-10-19. Codes and steps can vary by model; check your owner's manual.