Mitsubishi Mini Split P6 Error Code – Meaning, Causes & Fix
Mitsubishi mini split error code P6 is a drain pump fault or condensate water level protection error that appears on Mitsubishi Electric ductless mini split systems when the indoor unit's control board detects that the condensate water level in the drain pan has risen above the safe threshold. Mitsubishi mini splits equipped with a built-in drain pump (typically ceiling cassette and built-in duct models) use a float switch to monitor water level. When the float switch activates — indicating the pan is nearing overflow — the system displays P6 and shuts down cooling or heating to prevent water damage. On wall-mounted models without a drain pump, P6 can indicate a blocked condensate drain line. P6 is one of the most common Mitsubishi mini split error codes and is almost always resolved by clearing the condensate drain or servicing the drain pump. This guide covers every cause and fix. For related HVAC system error codes, see our Carrier Furnace Error Code 31 guide and our Rheem Furnace Error Code 57 guide.
What it means
The condensate water level in the indoor unit drain pan has risen above the safe level, or the drain pump has failed. The system has shut down to prevent water overflow damage.
Severity
ModerateCan you fix it yourself?
Yes — clearing the condensate drain line or cleaning the drain pump resolves most P6 errors.
Call a technician when
Contact a Mitsubishi Electric service technician if P6 returns after clearing the drain, or if the drain pump motor has failed.
What Does P6 Mean?
Mitsubishi Electric mini split indoor units produce condensate water as a byproduct of the cooling and dehumidification process. This water collects in the indoor unit's drain pan and must be continuously removed via the condensate drain system.
Error code P6 is triggered when:
1. Condensate float switch activates: The water level in the drain pan rises high enough to trigger the float switch, signaling imminent overflow. This is the primary trigger for P6. 2. Blocked condensate drain line: The drain hose or drain pipe leaving the indoor unit is blocked with algae growth, debris, or a kink, preventing water from draining. 3. Failed drain pump: On models with a built-in condensate lift pump (required when the unit cannot gravity-drain), the pump motor has failed or the pump impeller is clogged. 4. Condensate pump check valve stuck: A stuck check valve in the drain pump system prevents water from being expelled. 5. Drain pan cracked or misaligned: On ceiling cassette units, a misaligned or cracked drain pan can trigger the float switch incorrectly. 6. Float switch failure: The float switch has failed in the triggered position, reporting high water even when the pan is empty.
For related HVAC condensate and water management faults, compare with the Carrier Furnace Error Code 31 guide which covers condensate drain blockages causing pressure switch faults, and the Goodman Furnace Pressure Switch Stuck Open guide which describes similar drain-related sensor failures.
What Causes This Error?
- Condensate drain hose or pipe blocked by algae, slime, or debris
- Condensate drain hose kinked behind the unit or inside the wall penetration
- Drain pump motor failed — pump not running or not expelling water
- Drain pump impeller clogged with slime or debris
- Condensate pump check valve stuck in closed position preventing outflow
- Float switch failed in the activated (triggered) position
- Drain pan level uneven (ceiling cassette units) causing water to pool at the float
- Extremely high humidity operation causing condensate volume to exceed drain capacity
How to Fix P6
- 1
Power off the mini split and check the drain pan. Turn the mini split off at the remote control and at the circuit breaker. Open the indoor unit's front panel (on wall units, this lifts up; on cassette units, the grille panel drops down). Look into the drain pan at the bottom of the unit. If the pan contains standing water, the drain is blocked or the pump has failed. If the pan is empty and P6 appeared, the float switch may have failed.
- 2
Clear the condensate drain line. Locate the condensate drain outlet — typically a white PVC or vinyl hose exiting the indoor unit through the wall. At the drain outlet end (at the outdoor wall or where it drains), use a wet/dry vacuum to suction the line clear. Alternatively, disconnect the hose near the unit and gently blow compressed air through it. Flush with a diluted bleach solution (1 tablespoon bleach per cup of water) to kill algae and prevent future blockages. This step resolves most P6 errors on gravity-drain wall-mount models.
- 3
Clean the condensate drain pump (models with a built-in pump). On Mitsubishi units with a built-in lift pump (check your model's installation manual), locate the pump compartment inside or adjacent to the indoor unit. Remove the pump cover and clean the pump impeller and housing with warm water. Check the outlet tube from the pump for blockages. Verify the pump is receiving power by checking whether it hums when the unit tries to run (with the pan reset). Replace if the motor is silent and not running.
- 4
Check the condensate hose routing. Trace the full path of the condensate drain hose from the indoor unit to its termination point. Look for any sharp bends, kinks, or sections that run uphill — condensate will not drain against gravity without a pump. Ensure the hose has a consistent downward slope of at least 1/100 throughout its run. Correct any kinks or uphill sections.
- 5
Check the float switch. With the drain pan empty and dry, locate the float switch inside the drain pan — a small plastic float on a rod or lever. The float should sit at the bottom of its travel when the pan is empty. If it is stuck in the raised position, gently free it. Test by manually raising the float — you should hear the system respond (it will prevent the unit from starting while raised). If the float is stuck raised even when manually moved to the down position, replace the float switch.
- 6
Reset and test the system. After clearing the drain and servicing the pump, close all panels and restore power at the circuit breaker. Power on the mini split and run a cooling cycle for 15–20 minutes. Observe the drain pan — condensate should be visible draining continuously from the unit. If the drain hose shows regular dripping at the outlet and P6 does not reappear, the fault is resolved. Run for 30 minutes to confirm sustained normal operation.
When to Call a Professional
Mitsubishi mini split P6 that returns after clearing the drain and cleaning the pump indicates a failed drain pump motor or a failed float switch. Both components require accessing the indoor unit's internal components and are best serviced by a Mitsubishi Electric Diamond Contractor. Contact Mitsubishi Electric at mitsubishicomfort.com/support or 1-800-433-4822. Drain pump replacement costs $150–$350 including labor. Note that neglecting P6 can result in water damage to walls and ceilings — address this fault promptly.
Can You Still Use the Device?
The Mitsubishi mini split shuts down when P6 is active to prevent condensate overflow and water damage to the indoor unit and surrounding structure. Do not attempt to reset and run the system repeatedly while P6 is active — the drain pan will overflow. Resolve the drain fault before resuming operation.
See Also
Official Resources
Related Error Codes
Disclaimer: This article is for informational purposes only and does not constitute professional repair advice. CodeExplain is not affiliated with Mitsubishi or any other brand mentioned. Always consult a qualified technician for complex repairs.