Mitsubishi Electric code P5

Mitsubishi P5: the drain protection stopped the unit before water did

Mitsubishi P5 reports drain pump or overflow protection on the indoor unit. Read what the float switch proved, what it did not, and where owner checks stop.

Source verifiedBy HVAC Bench Editorial DeskLast reviewed
Direct answer

What this means

P5 is a drain protection stop on a Mitsubishi Electric indoor unit. The control saw the float switch rise, or it saw the drain pump circuit fail to respond, and it shut cooling down to keep the condensate tray from overflowing. The code proves water did not leave the tray fast enough. It does not name the blockage, the pump, or the switch as the failed part.

Equipment and model context

Mitsubishi Electric indoor units that publish the P-series protection table, including Mr Slim cassette, ducted, and ceiling-suspended indoor units

  • PLA-A series cassettes
  • PEAD-A series ducted indoor units
  • PCA-A series ceiling suspended indoor units

P5 is read here from the Mitsubishi Electric fault-code reference for the indoor families that publish the P-series table. Wall-mounted units without a condensate pump do not carry the same detection, and a Mitsubishi Electric controller fitted to another manufacturer's indoor unit will not follow this table. Match the code to the indoor unit model on its own rating label rather than to the outdoor unit.

What you may notice

  • Cooling stops while the indoor fan keeps running, and the controller or the operation lamp shows P5 with the indoor address.
  • Water is visible at the front of the cassette panel or at a ducted unit access hatch before or after the code appears.
  • The unit runs in heating or fan mode without complaint but stops within minutes of a cooling call.

Likely causes

  • The condensate path can fill faster than it drains when the drain line, the trap, or the drain hose falls out of its designed gradient.
  • The float switch can rise because the tray is holding water, and it can also rise because its own mechanism or wiring no longer reports a clear level.
  • The drain pump can stop moving water without failing outright, for instance when its inlet strainer is loaded.

Diagnostic paths

Cooling stops within minutes, and the drain outside is dry

Cooling starts normally, then P5 appears and stops it, while the outdoor end of the condensate line shows no water during a period when the coil should be producing it.

Leave the system off in cooling and switch to fan only so the coil dries. Report that the external drain stayed dry, which separates a blocked path from a pump that never received a start signal.

Water has already reached the ceiling or the cassette panel

Staining, dripping, or a swollen ceiling tile appears near the indoor unit, whether or not the P5 code is still on the controller.

Isolate the indoor unit at its own switch and stop using it in cooling. Water near an electrical enclosure is a service condition, not a drying-out exercise.

P5 arrives only in humid weather or at high fan speed

The unit runs for days without a code and then stops on P5 during muggy conditions, when the coil condenses more water per hour than at other times.

Record the outdoor conditions, the set point, and the fan speed in use, then have the drain gradient and pump lift checked against the installation manual rather than the pump replaced.

The four things P5 sits on top of

Four stages sit under this protection, in order: the coil makes condensate, the tray collects it, the pump lifts it, and the level switch reports the result. P5 is the report from the last stage, not a diagnosis of the first three.

  1. CoilProduces condensate while cooling
  2. TrayHolds the water until it is removed
  3. Pump and lineLifts and carries the water away
  4. Float switchReports the level the control acts on
What a P5 stop separates on a Mitsubishi indoor unit
What you observeSupported readingOwner action
Drain runs, code still appearsLevel detection or its wiring is in questionLeave the code on the controller for service
Drain dry during coolingWater is not leaving the trayStop cooling and report the dry drain
Pump audible, no dischargeLift or the pump inlet is restrictedDo not open the pump housing
Ceiling staining presentCondensate has already escapedIsolate the indoor unit and call service

P5 is a protection, so it fires before the damage

Mitsubishi Electric groups P-series entries as protection detections rather than component failures, and P5 belongs to the drain side of that group. The control does not measure a blockage. It measures a level, or the absence of the response it expected from the pump circuit, and it removes the load that was producing water. Reading P5 as a failed pump skips the question a technician has to answer first, which is whether the water had anywhere to go.

That distinction changes what a homeowner should do. A stopped compressor with a dry indoor unit is a system doing its job. The useful response is to stop asking for cooling, let the coil dry, and preserve the evidence. Restarting again and again refills the tray each time, which turns a contained protection event into water in a ceiling void.

Why the same code appears on a healthy pump

A cassette or ducted indoor unit lifts condensate against gravity before it reaches a gravity-fed run. The installation manual sets a maximum lift and a minimum fall for the run that follows, and both of those are properties of the pipework rather than of the pump. When either drifts, for example after building work moves a drain run or a trap dries out, the pump can operate correctly and still lose the race against a coil that is condensing hard.

Humidity is the variable that exposes it. Equipment that has drained for two years can stop on P5 in a wet week because the condensate rate rose while the drain capacity did not. Recording the weather, the set point, and the fan speed alongside the code gives service a reason to measure the drain arrangement rather than order a part. The condensate float switch reference explains the same protection logic across equipment types, and the mini-split condensate drain check covers what an owner can inspect without opening anything.

Service handoff

What to give the technician

Service needs the indoor unit model from its rating label, the P5 code with the address shown on the controller, whether the external drain discharged, the outdoor conditions when it stopped, and any history of building work that moved the drain run.

Homeowner safe

Safe homeowner checks

  1. Switch the indoor unit to fan only or off so the coil stops producing condensate, and leave it that way until the fault is assessed.
  2. Look at the visible outdoor end of the condensate line during a period when the unit had been cooling, and note whether any water discharged.
  3. Photograph the controller showing P5 together with the indoor unit address, and note the outdoor temperature and humidity at the time.

Is a reset appropriate?

A P5 stop clears when the level detection returns to normal, so a reset that appears to work has only emptied the tray. Treat a second occurrence as confirmation that the drain path needs measuring.

Stop point

When to call a technician

  • Checking the float switch, testing the drain pump circuit, and clearing a condensate line inside the indoor unit require the electrical enclosure to be opened, which is qualified service work.
  • Water staining on a ceiling, a wall, or an electrical accessory near the unit is a stop condition. Isolate the indoor unit and arrange service rather than running it to see whether the code returns.

Questions people ask about this

Does P5 always mean the drain pump has failed?

No. The reference entry covers the drain protection detection, which can be raised by the level switch or by the pump circuit. A restricted line, a lost gradient, or a loaded pump inlet can produce the same stop with a pump that still runs.

Can I keep cooling while I wait for service?

Running in cooling refills the tray that triggered the protection. Fan-only or heating operation does not condense water on the indoor coil, so it is the safer way to keep air moving until the drain arrangement is checked.

Why does P5 only appear in humid weather?

Condensate production rises with indoor humidity, so a drain path with marginal capacity can cope in dry conditions and fall behind in wet ones. That pattern points the investigation at the pipework rather than at the pump.

Is P5 the same on every Mitsubishi indoor unit?

It is defined for the indoor families that publish the P-series table. A wall-mounted unit with no condensate pump does not carry the same detection hardware, so confirm the indoor model before applying this reading.

Evidence record

How this page was checked

official manufacturer support article · checked 2026-09-15

Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Mitsubishi Electric and Mitsubishi Electric Trane HVAC US technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.

Documentation class
official manufacturer support article
Scope of the definition
Mitsubishi Electric indoor units that publish the P-series protection table, including Mr Slim cassette, ducted, and ceiling-suspended indoor units
Last checked
2026-09-15