Mitsubishi Electric Drain Pump Code
Mitsubishi P5 Error Code
Seeing the Mitsubishi P5 error code usually means water is not leaving the indoor unit fast enough. On Mitsubishi Electric cassettes and ducted systems, P5 is drain overflow protection. The unit stops cooling so the drain pan does not spill into your ceiling. Here is how to understand it and what to do next.
Meaning
What Is Mitsubishi Electric Telling Me With P5?
P5 is a protection code tied to the drain system. Service manuals call it drain overflow protection operation, while some wireless remote tables simply call it a drain pump error. Both labels describe the same event from slightly different angles.
Here is what happens. The drain pump runs to lift condensate out of the pan. A float switch watches the water level beside it. If the float stays high for a sustained period while the pump is supposed to be working, the board concludes the water is not draining. It pauses cooling, keeps the pump running, and watches again. If the float rises once more, P5 locks in.
In short, P5 means the switch is working fine but the water is not going anywhere. That points the investigation at the pump, the pipe and anything blocking either of them.
Maker
Mitsubishi Electric. Mitsubishi Heavy Industries has its own drain code in its numbered E list, and P5 on an MHI unit would not carry this meaning.
Units
Indoor units with a drain pump and float switch, chiefly ceiling cassettes and ducted models. Gravity drained wall splits usually do not raise P5.
Trigger
The float reads high water for a sustained period while the pump runs, then again after the unit pauses cooling to let the pump catch up.
The Difference
How Is P5 Different From P4?
The two codes sound alike, yet they point in different directions. Getting this right saves time on the day.
P4 Means the Switch Signal Is Missing
With P4, the board cannot see the float switch circuit at all. The problem is usually a plug, a lead or the switch itself. Water may or may not be present.
P5 Means Water Is Building Up
With P5, the board can see the switch perfectly, and the switch is telling it the water level is high. The likely suspects are the pump, a blocked pipe or sludge in the pan.
Occasionally both codes appear in the error history. That can happen when a float sticks, or when debris affects both the float and the pump. The technician will read the history and work out which came first.
On Screen
How Do I Know My Unit Is Showing P5?
On a wired wall controller, the letters P5 normally appear on the display, sometimes with a unit address. Ducted and cassette systems mostly use this style of controller, so you will often see the code plainly.
If you only have a wireless remote, the self check mode is useful. In general terms, you enter check mode, point the remote at the receiver and count the replies. Many Mitsubishi Electric cassette and ducted manuals pair P5 with five beeps and five lamp flashes.
Be aware that one other code shares that five beep pattern on some ranges. PA, a forced compressor stop linked to water leakage, can also produce five beeps. A wired controller or the technician’s check will tell them apart, so mention the count when you call.
Root Causes
Why Is My Mitsubishi Drain Pump Not Keeping Up?
Mitsubishi Electric service documents highlight a short list of usual suspects. Here they are, from the usual and simple to the less likely and more involved.
Water Path Problems
- Slime, dust and biological growth clogging the pump inlet.
- A drain pipe blocked by sludge, insects or debris.
- A pipe that sags and holds water, so the pump cannot push past it.
- An outlet crushed, kinked or buried in a garden bed outside.
Component Problems
- The drain pump has slowed, stopped or seized.
- Debris holding the float up, giving a false high reading.
- A damaged pump lead or poor connection to the board.
- The indoor controller board failing to drive the pump, the least common cause.
Most P5 calls end up being sludge or a blocked pipe. Condensate is a perfect home for slime, especially when filters are not cleaned regularly. Over time that slime finds its way into the pump and the line, and the water backs up.
Safe Steps
What Can a Homeowner Check With P5?
There are a handful of safe things you can look at from outside the unit. They help the technician and sometimes reveal an obvious cause.
Switch Off and Contain
Turn the system off at the controller. If water is dripping from a cassette, place a bucket and towels underneath and switch off at the breaker.Find the Drain Outlet
Walk outside and find where the condensate pipe ends. It often discharges near a downpipe, garden bed or tundish. Check that the end is not crushed, buried or blocked by leaves.Watch for Dripping
When the system ran normally, that outlet would drip steadily in cooling. If it was dry while P5 appeared, the water is stuck somewhere upstream.Check the Filters
Clean dirty filters. They do not cause P5 directly, but clogged filters feed more dust into the pan and speed up sludge build up.Record Everything
Note the code, any beep count, the unit address, the date and any staining. Take photos of ceilings around the unit.
That is the limit of owner checks. Do not open the cassette panel, pour chemicals into the pan, or try to blow out the drain line with compressed air. Each can damage the pump or push water where it should not go.
Technician Work
What Does a Technician Do to Clear P5?
A technician treats P5 as a drain system investigation. They want to know whether the pump is lifting water and whether the pipe is carrying it away.
- Read the error history and note related entries such as P4 or P6.
- Run the drain pump test from the controller service menu, which is protected for technician use.
- Open the unit, inspect the drain pan and clear sludge from the pump inlet.
- Unplug and test the float switch in its raised and lowered positions.
- Check the pump feedback and speed, since this is a DC pump driven by the indoor board.
- Trace the drain line for sags, uphill sections, crushes and blockages, then flush it clean.
- Replace the pump if it is slow or seized, matching the correct part to the model.
- Consider the indoor board only after the pump, switch and pipe all test normal.
Once fixed, the technician runs the system and pours water into the pan to prove the pump starts, lifts and clears it. That final test confirms the whole drain chain is working again.
Risk Check
Is It Safe to Run the Unit After a P5 Code?
The honest answer is no, not until the drain is sorted. P5 exists to stop water overflowing. Forcing the system back into cooling simply produces more condensate with nowhere to go.
On a cassette, that water can drip straight through the grille onto floors and furniture. On a ducted unit, it can overflow into a safety tray, or worse, into the ceiling below. Plasterboard and insulation do not cope well with repeated soaking.
Heating is a slightly different story, because heating mode produces little or no condensate indoors. Even so, it is wise to leave the system off until a technician has checked the pump. A seized pump can also overheat, and you do not want it running dry for days.
Climate Factor
Why Does P5 Show Up More in Humid Summers?
Humidity is the big driver. The more moisture in the air, the more water the indoor coil produces. During a sticky Brisbane summer, or a humid run of days in Sydney, a cassette can generate a surprising volume of condensate in an afternoon.
A pump that copes in drier weather may struggle when it is working flat out. If sludge has partly narrowed the inlet, that extra load is often what tips it over into P5. That is why many owners see P5 for the first time during a muggy week rather than a dry heatwave.
Warm ceiling spaces also encourage biological growth in the pan. In Perth and Adelaide the air is often drier, yet long cooling seasons still give slime plenty of time to build. Melbourne systems see the problem too, particularly in humid late summer spells. Regular servicing keeps pans and lines clean in every city.
Prevention
How Can I Stop P5 Coming Back?
Unlike many codes, P5 responds well to routine care. Most of the causes build up slowly, so steady maintenance keeps them in check.
Clean Filters Often
Dust that slips past a dirty filter lands on the wet coil and washes into the pan. Clean filters monthly during heavy use, and more often in dusty or smoky periods.
Book Regular Services
A professional service can include cleaning the drain pan, clearing the pump inlet and flushing the line. That removes sludge before it causes trouble.
Protect the Outlet
Keep the external drain outlet clear of mulch, soil and leaves. Make sure gardeners know not to bury or crush it.
Watch the Drip
Every so often during cooling, check that the outlet is dripping. A dry outlet on a humid day is an early sign of a blockage upstream.
After the Leak
What Should I Do About Water Damage After P5?
Sometimes P5 arrives after water has already escaped. A cassette might have dripped onto carpet, or a ducted unit might have marked the ceiling below. Dealing with that promptly limits the damage and makes the repair visit easier.
- Turn the system off at the breaker before touching anything wet near light fittings or power points.
- Soak up standing water with towels and move furniture, rugs and electronics out of the drip zone.
- Photograph stains and wet areas for your records and any insurance discussion.
- Open windows or run a fan to help damp areas dry out.
- Keep an eye on ceiling stains for sagging, which can mean water is pooling above the plaster.
- Tell us about any damage when you book, so the technician can check the safety tray and nearby insulation.
Air conditioning technicians focus on the system itself. If ceilings or floors are badly affected, a building or restoration trade may also be needed. The technician can point out what they see, but plaster repairs and carpet drying sit outside an air conditioning job.
Above all, do not restart cooling to test whether the leak has stopped. Each cooling run adds more water. Wait until the drain has been cleared and proven before switching back on.
Related Codes
Which Mitsubishi Codes Are Linked to P5?
Drain faults rarely live alone. These related codes help paint the full picture of what your system is doing.
P4 Float Switch Circuit
The board cannot see the float switch at all, usually a plug, lead or switch fault.
P6 Coil Protection
An iced coil can thaw into the pan in a rush, overwhelming the pump later.
Mitsubishi Code Hub
See every confirmed Mitsubishi Electric and MHI code we have written up.
For other brands, visit the main error codes library.
Booking
How Do I Get a Technician for P5 in My City?
Rapid Air Cooling arranges the repair and sends an independent licensed technician. We are not a Mitsubishi dealer and hold no manufacturer accreditation. The technicians we dispatch hold the licences their work requires.
Pick your city. Sydney owners can use our Sydney repairs page, and Melbourne owners can use air conditioner repairs Melbourne. Queenslanders will find Brisbane repairs and our Brisbane Mitsubishi page. Over west, see Perth repairs and Mitsubishi in Perth. In South Australia, use Adelaide repairs.
Our national Mitsubishi air conditioning page explains the brand range, and the troubleshooting library covers leaks and other symptoms. You can also read about our air conditioning service Australia wide.
Good to Know
Are There Any Lesser Known P5 Details?
Open more detail
The drain pump on these units is typically a small DC motor driven by the indoor board. Because it is a DC pump, technicians check its speed and feedback rather than relying on a simple resistance test. That is one reason P5 diagnosis needs proper tools.
Drain lines on cassettes often rise straight up from the pump before falling away to the outside. If that rise is too tall, or the fall afterwards is too flat, water can slide back into the pan after the pump stops. That can create repeat P5 faults that no amount of cleaning will cure. A technician can spot this and suggest a correction.
After a pump replacement, ask the technician whether the drain pan and line were also cleaned. Fitting a new pump into a sludgy pan simply gives the slime a fresh target. A full clean at the same visit gives the new pump the best start.
Finally, if a ducted unit has a secondary tray beneath it, that tray may have its own outlet. Keeping that outlet clear is part of good maintenance, and it gives you a backup if the main drain ever struggles.
Questions
Frequently Asked Questions
Does P5 always mean the drain pump is broken?
No. A blocked pipe or sludge around the pump inlet causes P5 just as often. The pump may be perfectly healthy once the blockage is cleared.
Can I clear the drain line myself?
You can check the outside end is not crushed or buried. Anything beyond that, including flushing the line or opening the unit, should be left to a technician to avoid damaging the pump.
Why did P5 appear on a very humid day?
Humid air produces far more condensate. A pump or pipe that is partly restricted may cope on dry days but fall behind when the water volume jumps.
Will heating mode work with a P5 fault?
Heating produces little indoor condensate, so the unit may seem fine. Still, the fault remains, and it will return as soon as cooling starts. Book a repair before summer.
Is P5 used on Mitsubishi Heavy Industries air conditioners?
Not with this meaning. MHI lists drain trouble under its own numbered E code. Check the brand badge before relying on this page.
My wall split shows five flashes. Is that P5?
Not necessarily. Lamp patterns on MSZ wall splits follow a different table from cassette and ducted self checks. Note the exact pattern and the model number when you book.
How often should drain pans be cleaned?
It depends on use and dust levels. Many homes have the pan checked at each regular service. Heavily used cassettes in humid areas benefit from more frequent attention.
Water Backing Up With a P5 Code?
Switch the system off and call us. We will book a licensed technician to clear the drain and test the pump.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles