What happens
The lift pump cannot remove water or its sensing/control circuit reports an incorrect level.
Typical symptoms
Intermittent shutdown, pump noise, high water level or leakage where gravity drainage is not possible.
Checks that distinguish this cause
Identify the installed pump, power supply, lift limit and interlock arrangement. Safely inspect sensing movement and evaluate the documented pump test, including water discharge rather than motor sound alone.
What can look similar
A blocked discharge hose or incorrect lift can overload a healthy pump.
Repair direction
Repair the established routing or electrical problem, or fit an approved pump or sensor while preserving overflow protection.
Verify the repair
Verify water removal and the documented high-level shutdown response.
Equipment-specific limits
Drain lift, hose routing, traps, vents and overflow wiring differ by indoor style and pump. Do not bypass overflow protection or assume a high-wall drain design suits a cassette.
Practice this diagnosis
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- Senville: R-454B model documentationSeparate installation and service documents for indoor styles and multi-zone generations.
- Haier: Arctic Next Gen service manualAW/1U EH2VHD model examples of inverter, motor, sensor and circuit diagnostics; obtain the installed model manual.
Editorial review: 2026-09-29. Verify the current manual for the installed model.