Air-con condensate pump not working / unit shut down on overflow
An aircon has shut down on a condensate overflow/float switch, or its condensate pump isn't running — water isn't being removed, so the unit stops to prevent overflow.
Safety first
Water + electrics — isolate before working. An overflow can damage ceilings/property. The float/safety switch is doing its job by shutting the unit down.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Blocked condensate drain
Most likelyA blocked/algae-fouled drain backs water up and trips the float switch.
- 2
Condensate pump failed / no power
#2The pump that lifts condensate has failed or lost supply.
- 3
Float / safety switch fault or stuck
#3The float switch is stuck or faulty, shutting the unit down (or not protecting it).
- 4
Pump wiring/interlock fault
Least likelyThe pump/interlock wiring to the unit is faulty.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeCheck the condensate drain/tray for blockage and the water level.
Clear drain; normal water level.
Drain clear — check the pump and float switch.
Blocked drain — clear it (then the float should reset).
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Condensate overflow / pump fault
→ step 2 - 2decision
Is the condensate drain clear (not blocked)?
Yes→ step 3No→ step 4 - 3decision
Do the pump and float switch operate correctly?
Yes→ step 5No→ step 6 - 4result
Clear the drain; the float should reset.
- 5result
Check the pump/interlock wiring to the unit.
- 6result
Failed pump or stuck/faulty float — rectify/replace.
Common mistakes apprentices make
- Clearing the float trip without clearing the actual drain blockage.
- Not checking the condensate pump has power/runs.
- Overlooking a stuck float switch.
- Leaving an overflow risk that can damage property.
When to stop & escalate
Pump/float/interlock electrical work is licensed; drainage/mechanical clearing may involve the refrigeration/mechanical tech. Persistent overflow needs the drainage design checked.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
Ducted air-con system has no power / won't start
A ducted system (roof/cupboard fan unit + zones/controller) is dead or won't start — pointing at the dedicated supply/isolator, the controller, zone motors, or the unit's PCB.
Split-system air-con not running at all
A split-system (head unit + outdoor condenser) is completely dead — no response from the remote/controller — pointing at supply, isolator, controller, or the indoor PCB.
Float / level switch not operating
A float or level switch isn't controlling correctly — a pump won't start/stop on level, a tank overfills or runs dry, because the level switch isn't changing state.
Learn the theory
How the gear and circuits behind this fault actually work.