Mitsubishi Electric PA fault codewhat it means and how to fix it
A drain fault. Mitsubishi tell their own engineers not to assume the pump has failed — the usual cause is a blockage backing the water up.
Take care
What PA means
PA is a drain fault and P5 is a high condensate level in the drip tray, and they are the two most owner-relevant codes Mitsubishi publish on air conditioning. Both are triggered the same way: a float switch detects that water is standing where it should not be, or a drain sensor finds itself immersed, and the system stops rather than letting your ceiling or your wall take the consequences. So the code is protection working rather than a component announcing its own failure. What makes these worth a page is Mitsubishi's own note to engineers, which is unusually direct and will save you money if you know it before somebody quotes. Their words: do not assume the drain pump is faulty here — on Mitsubishi equipment the drain pump runs whenever the unit is in cooling mode, it is a very reliable and robust piece of equipment and does not often fail, and the most common cause is a drain pipe or drip tray blockage causing the water to back up, so inspect the drip tray, the drain pipe and the float switch or sensor before ordering parts.
For the high level code they add that you should clean the drains out and then reboot the power to the outdoor unit to clear the fault, noting again that the pump runs constantly in cooling mode. That is a manufacturer explicitly warning against the obvious and expensive diagnosis. The service manuals fill in the timings and the difference between the two codes. P5 is drain overflow protection: the unit suspends itself if the float switch has been under water for a minute and a half continuously with the pump running, stops the compressor and the indoor fan, and confirms the fault if it happens again. PA is the escalation Mitsubishi call a forced compressor stop due to a water leakage abnormality, raised when the float switch has been in the water for more than fifteen minutes while the coil has been running cold for a total of half an hour, and their note is that once it has been detected the abnormality is not released until the main power is reset.
So P5 is the tray filling and PA is the tray having stayed full — which is also why the lookup’s remedy is a power reboot rather than a button on the controller. It matters which unit you have. These codes belong to units with a condensate pump and float switch: ceiling cassettes, ducted units and wall units fitted with an optional pump. The ordinary domestic wall-mounted MSZ units drain by gravity through a hose, have no pump and no float switch, and cannot raise either code; on those, water on the wall is a hose problem and there is no code to read. There is a third code in the family that separates cleanly from these two. A drain sensor fault is published where the tray is clear but the sensor itself is reading wrongly, and Mitsubishi note that an open circuit or a short circuit on the sensor produces it. They also make a practical point that matters when someone attends: check the wiring diagram to see whether the indoor unit has a float switch or a sensor, because the two are different components and the machine does not tell you which it has. What is yours in all of this is the outside end of the condensate pipe. Everything upstream of it is inside a unit carrying mains voltage.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| A blocked drain pipe | Mitsubishi’s named most common cause. The water has nowhere to go, backs up into the tray, and lifts the float switch. | Common |
| A blocked or fouled drip tray | Also named. Dust drawn from the room mixes with condensate into a sludge that closes the tray outlet before the pipe itself blocks. | Common |
| The outside end of the pipe obstructed | Leaves, algae, insects and nests block a condensate outlet, and this is the part of the path an owner can actually inspect. | Common |
| A drain sensor fault with a clear tray | Mitsubishi publish this separately and note that an open or short circuit on the sensor causes it. The tray is fine; the reading is not. | Occasional |
| A genuine pump failure | Possible but uncommon, and Mitsubishi say so themselves. It should be the conclusion after the tray and the pipe have been checked, not before. | Occasional |
What to try yourself
Switch the system off so nothing is adding water while you look at it.
Find where the condensate pipe leaves the building, usually near the indoor unit, and check the outlet is clear.
Check the pipe falls continuously to that outlet. A sagging or lifted section holds water and stops everything behind it draining.
Note whether you have PA, P5 or the drain sensor code. A clear tray with a sensor fault is a different repair from a blockage.
When you book an engineer, ask them to check the tray, the pipe and the float or sensor before ordering a pump. That is the manufacturer’s own instruction to them.
Do not open the indoor unit to reach the tray yourself.
The drip tray sits directly beneath the coil, alongside the fan motor and mains wiring. There is already water in there and adding yourself to the situation is the wrong move.
Get an F-Gas certified heat pump engineer to look at your Mitsubishi Electric PA
We do not pass enquiries to a repair firm, so there is no form here. When you book an F-Gas certified heat pump engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£80–£280
Time on site
45 minutes
A drain clear and service is the usual outcome. A float switch or drain sensor costs more, and a pump — which the manufacturer says is uncommon — more again.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Mitsubishi Electric fault codes
- 2503Get it checkedA drain sensor fault, which is the version where the tray is clean. Mitsubishi note the indoor unit may have a float switch instead of a sensor.Related: condensate and water
- U1Get it checkedU1 is a high-pressure fault on a Mitsubishi air conditioner and on an Ecodan alike. The fault is the same; the checks depend on which appliance you have.Related: same brand
- EFUsually simple to fixA non-defined error that Mitsubishi attribute to noise interference, with a published owner remedy: power down for thirty seconds.Related: same brand
Own a Mitsubishi Electric air conditioner? Save it and its codes come first next time.
Related guides
Common questions about Mitsubishi Electric PA
The engineer says I need a new pump.
Ask whether the tray and drain pipe were checked first, because Mitsubishi’s own guidance to engineers is not to assume the pump is faulty. Their stated position is that the pump runs whenever the unit is cooling, is robust, and does not often fail, and that a blockage backing the water up is the most common cause.
What is the difference between PA and P5?
They are close relatives. PA is published as a drain fault and P5 as a high condensate level in the drip tray, and both are triggered by a float switch detecting standing water or a sensor being immersed. The service manuals put timings on them: P5 after the float has been under water for a minute and a half with the pump running, PA after more than fifteen minutes, and PA is held until the main power is reset. In practice they lead to the same checks — tray, pipe, float or sensor.
I have a wall-mounted unit. Does this apply to me?
Only if it has a condensate pump fitted, which most domestic wall units do not. Mitsubishi’s MSZ wall units drain by gravity through a hose and have no float switch, so they cannot raise PA or P5; their fault table has no drain entry at all. Water from one of those is a hose that is blocked, kinked or running uphill, and Mitsubishi’s owner instruction for water dripping from the indoor unit is to stop using it and consult the dealer.
The tray is clean but it still reports a drain fault.
That fits the separate drain sensor code, which Mitsubishi publish for exactly this case. Their note is that if the drip tray is clear, an open or short circuit on the drain sensor can cause the fault. Worth mentioning, because it points at a component rather than a clean.
Can I clear the code myself?
Mitsubishi’s published route for the high level code is to clean the drains out and then reboot the power to the outdoor unit. The cleaning part is the bit that matters — clearing the code without clearing the blockage just means it comes back on the next humid day.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer support portal
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.