What this code means
E5 on a Mitsubishi mini-split indoor unit indicates a drain pump fault or a drain float switch activation. On units equipped with a condensate lift pump (used when gravity drainage is not possible), the control board monitors the pump and the float switch in the drain pan. E5 triggers when the pump circuit faults or the float rises to the high-water mark, signaling that water is not being removed from the drain pan.
Common Causes
- Blocked condensate drain line — Algae, mold, or debris clogging the drain hose causes water to back up in the pan, raising the float and triggering E5.
- Failed drain pump — The condensate pump motor burns out or seizes, stopping drainage entirely. Water accumulates and activates the float switch.
- Float switch stuck or mispositioned — The float switch can get stuck in the raised (tripped) position due to debris or physical obstruction in the pan.
- Drain line installed with insufficient slope — A flat or back-pitched drain hose won’t flow by gravity and causes recurring blockages.
Step-by-Step Fix
- Inspect the drain pan — Remove the indoor unit front panel and look into the drain pan. If water is present, the drain line is blocked or the pump is not running.
- Clear the drain line — Disconnect the drain hose and blow it out with compressed air, or use a drain cleaning brush. Flush with a dilute bleach solution (1 tablespoon bleach per gallon of water) to clear algae.
- Test the condensate pump — With power on and water in the pan, confirm the pump runs (you should hear a hum or see water flowing through the discharge line). If silent with water present, test pump voltage — if voltage is correct but pump is silent, replace the pump.
- Check the float switch — With the pan empty, the float should be down and the switch should be in the normal (un-tripped) position. Manually lift and release the float to confirm it moves freely and the switch clicks.
- Clear the E5 fault and test — Power cycle the indoor unit. Confirm the drain pan is empty, the pump runs, and the drain line flows freely before restarting.
Parts Often Needed
| Part | Notes |
|---|---|
| Condensate drain pump | Amazon | Match Mitsubishi model and voltage; many are 115V |
| Float switch | View on Amazon | Often sold with pump kits |
| Drain hose (flexible) | Amazon | Replace if kinked or biologically fouled |
| Drain pan tablets (algae inhibitor) | Amazon | Preventive maintenance; reduces future blockages |
When to Call a Pro
If drain water is leaking into the wall or ceiling cavity, a licensed HVAC technician should assess the drain line routing and ensure no structural damage has occurred. Persistent mold in the drain pan may require unit disassembly to clean.