P5
Mitsubishi Electric Split AC
Severity: MinorWhat Does This Error Mean?
P5 on a Mitsubishi Electric AC means the indoor unit float switch has detected that water in the drain pan has risen too high. This happens when the drain line is blocked or the drain pump has failed, causing condensation water to back up. The AC shuts down to prevent water overflowing into the room or into the ceiling.
Affected Models
- Mitsubishi Electric MSZ-AP Series
- Mitsubishi Electric MSZ-EF Series
- Mitsubishi Electric MSZ-GL Series
- Mitsubishi Electric Cassette AC (ceiling type)
- Mitsubishi Electric Ducted AC
Common Causes
- Drain pipe blocked with algae, mould, or debris
- Drain pump motor failed or impeller jammed
- Float switch stuck in the raised position (false P5)
- Drain pipe routed incorrectly — upward section preventing gravity flow
- Drain pipe disconnected or cracked, letting water escape in the wrong place
How to Fix It
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Switch off the AC immediately.
Check the area below and around the indoor unit for water dripping or pooling — P5 means the drain pan is close to or at overflow level.
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Locate the condensate drain pipe exit point.
Follow the drain pipe from the indoor unit to where it exits outside or empties into a household drain. Check whether water is flowing out — if the pipe is blocked, no water will be coming out.
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Clear the drain blockage.
Use a wet/dry vacuum at the pipe exit end to suck out blockages. Alternatively, blow compressed air gently through the pipe from the exit end back towards the indoor unit. Do not use high-pressure air — it can crack PVC drain fittings.
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Flush the drain pipe with clean water.
Pour a small amount of clean water into the drain tray access point to confirm the pipe is now flowing freely.
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Restart the AC and monitor.
P5 should clear once the drain pan empties. If P5 persists after the drain is clear, the float switch or drain pump needs inspection by a technician.
Frequently Asked Questions
How do I prevent P5 from happening again?
The main cause is a blocked drain pipe. Pour one tablespoon of household bleach diluted in a cup of water into the drain tray once a month during the cooling season. This kills algae and prevents the slime buildup that causes blockages. Also ensure annual AC servicing includes a drain flush.
Does P5 only happen in humid weather?
P5 is more common during hot and humid periods because the AC produces more condensation when dehumidifying heavily. However, a blocked drain will eventually trigger P5 in any weather if the pipe is not maintained.