Honeywell MO08CESWK 8,000 BTU Compact Portable Air Conditioner E4 Error Fix: Water Tank Full — Unit Stopped

Error code E4 on the Honeywell MO08CESWK 8,000 BTU Compact Portable Air Conditioner means: Water Tank Full — Unit Stopped. The internal water collection tank is full and the unit has automatically shut off to prevent overflow — in cooling mode, the unit partially evaporates condensate through the exhaust but in high-humidity conditions the tank fills; drain the tank using the bottom drain plug into a shallow pan or attach a continuous drain hose; the unit will restart automatically once the float switch drops

The most successful fix is "Install Continuous Drain Hose to Prevent Frequent Tank Full Errors" (medium difficulty, ~30 minutes). Estimated DIY cost: $10-$20. HomeMD has 2 community-ranked fixes for this error.

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Yes — the top-ranked community fix ("Install Continuous Drain Hose to Prevent Frequent Tank Full Errors") is rated medium difficulty and takes about 30 minutes. Tools needed: Flathead screwdriver, Pliers.

DIY cost: $10-$20. Professional repair typically costs $100-$150. Many homeowners save money by trying the top-ranked community fix first.

The Honeywell MO08CESWK 8,000 BTU Compact Portable Air Conditioner has 8 other known error codes, including: CF (Clean Filter Reminder), E1 (Room Temperature Sensor Fault), E2 (Evaporator Temperature Sensor Fault), E3 (Condenser Temperature Sensor Fault), E5 (System Defect — Contact Service), and 3 more.

Error code E4 also appears on 1 other Honeywell model: MN14CCSBB 14,000 BTU Portable Air Conditioner with Dehumidifier and Remote Control. The fix may vary by model, so check each model's specific page for tailored repair steps.