What happens
The sensing mechanism or installation does not represent the intended water level.
Typical symptoms
Nuisance shutdown with a dry pan, or failure to stop before overflow.
Checks that distinguish this cause
With safe isolation, inspect movement, debris and mounting against the exact switch model instructions. Test its intended circuit interruption.
What can look similar
An intermittent backed-up drain may look dry by the time the technician arrives.
Repair direction
Clean, reposition or replace only as permitted by the manufacturer; preserve the safety function.
Verify the repair
Verify both normal drain operation and documented overflow shutdown.
Equipment-specific limits
The interrupted circuit differs by installation. Never bypass a float to keep cooling while water rises.
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.
- RectorSeal: Safe-T-Switch manufacturer resourcesOverflow-switch purpose and model-specific installation resources.
Editorial review: 2026-09-29. Verify the current manual for the installed model.