p4
Easy Fix
Mitsubishi Electric · Mini-Splits & Ductless Systems
Drain Sensor Fault
Quick Answer
Error code P4 on your Mitsubishi Electric Mini-Splits & Ductless Systems means: Drain Sensor Fault. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Check the condensate drain line for clogs and clear using compressed air or vacuum
2
Inspect the drain pan and float sensor for debris or buildup that could cause a false trigger
3
Clean the float sensor mechanism and verify it moves freely
4
Check the drain sensor connector at the indoor PCB
5
Verify proper drain line pitch for gravity drainage
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
Parts You May Need
Drain sensor
Condensate drain line cleaner
Float switch
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