Home › Air Conditioners › Mitsubishi Electric › P4 / P5
Mitsubishi Electric Air Conditioner P4 / P5 Error Code
Drain sensor or drain pump problem. Here is what it means and how to clear it, easiest fix first.
The indoor unit has found a problem with its condensate drain system. P4 points to the drain sensor or float switch, and P5 to the drain pump or a drain overflow. A clogged drain line, a stuck float or a failed pump is the usual cause.
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. These codes mainly appear on ceiling cassette and ducted units with a built-in drain pump.
How to fix Mitsubishi Electric P4 / P5
Switch off the power
Switch off the system at the breaker. If water is dripping near an outlet or light, switch off that circuit too and don't touch wet fittings.
Clear the drain line outlet
Find where the condensate line ends, outdoors or at a floor drain, and clear any dirt, algae or debris you can reach at the open end.
Clean the filters and reset
Wash the indoor filters, let them dry and refit them, then restore power and restart the unit.
When to call a technician
If the code returns, have a technician check the drain pump, float switch and internal drain pan.
Parts that commonly cause P4 / P5
- drain pump
- float switch / drain sensor
- condensate drain line
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
- PAShut down to prevent a water leak
- P6Freeze or overheat protection
- P8Pipe temperature error
- PbIndoor fan motor error
- FbIndoor control board 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 P4 / P5 mean on a Mitsubishi Electric air conditioner?
The indoor unit has found a problem with its condensate drain system. P4 points to the drain sensor or float switch, and P5 to the drain pump or a drain overflow. A clogged drain line, a stuck float or a failed pump is the usual cause.
Can I fix Mitsubishi Electric P4 / P5 myself?
Often. The first steps above are safe checks a homeowner can do. If they don't clear P4 / P5, the cause is likely a worn part that needs replacing.
What if P4 / P5 keeps coming back?
A code that returns after a reset and the checks above usually means a part is wearing out. Note when P4 / P5 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.