Aircon Drain Pan and Float Switch
This is the overview page for drain-pan and float-switch faults. These two parts sit in the same drainage path, but the root cause is often a blocked drain pipe or ice-related overflow.
What This Part Does
As your aircon cools a room, moisture condenses on the indoor coil. This condensate drips into the drain pan beneath the coil and flows out through the drain pipe to a waste point.
The float switch sits inside the drain pan. It monitors the water level. If the drain blocks and water rises too high, the float switch trips and shuts the unit down. This prevents overflow into the room or ceiling.
Together, the drain pan and float switch form the drainage safety system. The pan collects water. The switch prevents overflow. When both work correctly, you never know they are there.
How You Would Notice
The most common sign is water dripping from the front or bottom of the indoor unit. In ceiling cassettes, you may notice water staining on the ceiling tiles before the drip reaches you.
The unit may shut off on its own and refuse to restart. The float switch has tripped — the drain is blocked, water rose to the trip level, and the unit shut down to protect itself.
A musty smell without visible water can also indicate a partially blocked drain. Stagnant water in the pan encourages mould growth, which gets pushed into the room by the fan.
- Water dripping from the indoor unit or ceiling below it
- Unit shuts off and will not restart — float switch has tripped
- Musty smell from the unit even after servicing
It Might Not Be The Drain Pan
A refrigerant issue can cause the indoor coil to freeze. When the unit shuts down or defrosts, ice melts faster than the drain can handle and overflows the pan. This looks like a drain problem but the root cause is low refrigerant or a failing expansion valve.
A cracked or misaligned drain pan is less common but does happen on older units. The pan fills normally but water escapes through a physical gap rather than a blocked pipe.
A faulty float switch can also cause repeated unit shutdowns even when the drain is clear. The switch trips at the wrong level and stops the unit unnecessarily.
How We Check
We start with the drain pipe. We flush the condensate line to confirm it is clear and water flows freely to the waste point. A blocked drain accounts for the large majority of water leak complaints.
If the drain is clear, we check the drain pan for cracks, misalignment, or residue buildup. We also check that the pan is seated correctly under the coil — installation issues can shift it out of position over time.
We test the float switch by simulating a high water level. It should trip the unit reliably and reset cleanly when the water level drops.
If the drain and pan are fine, we check refrigerant pressure and coil temperature. Coil icing is the less obvious cause of overflow and needs to be ruled out.
What We Find And What Happens Next
Most water leak visits resolve with a drain flush. Genuine drain pan or float switch faults are less common but straightforward once the simpler causes are ruled out.
| Finding | Next Step |
|---|---|
| Drain pipe blocked | Flush drain, confirm flow, retest |
| Float switch faulty — tripping incorrectly | Replace switch, test reset behavior |
| Drain pan cracked or misaligned | Reseat or replace pan |
| Coil icing causing overflow | Check refrigerant and expansion valve |
About The Repair
A drain flush is a routine part of a general service. Severe blockages — heavy buildup or biological obstruction — may need chemical clearing rather than a simple flush.
Float switch replacement is a minor repair. The switch is a small sensor inside the drain pan. Access requires opening the indoor unit but is not a complex job on most unit types.
Drain pan replacement is less common. On newer units, pans are usually repairable or correctly reseated. On older units, a cracked pan sometimes cannot be sourced separately from the full indoor unit body.
After Replacement
After a drain flush or float switch replacement, we run the unit and confirm water drains freely. We watch the drain line at the exit point to confirm flow.
If a float switch was replaced, we confirm the unit starts, runs, and the switch resets correctly. A switch that resets but does not hold through a full cycle needs to be rechecked.
We also check for staining or residue in the pan that may indicate mould. Persistent mould means the drain was blocked long enough to allow growth — the pan may need separate cleaning.
When We Tell You To Wait
If water is dripping onto furniture, flooring, or electrical fittings below the unit, do not wait. Turn the unit off and contact us. Water damage from a prolonged leak is more expensive than the repair.
If the unit has shut off via the float switch and the room is not at risk, a scheduled visit is reasonable. The unit is protecting itself. Do not bypass the switch to force a restart.
Minor musty smell without visible water can be monitored through the next service cycle. If it persists after a drain flush, the cause is likely mould in the pan or coil rather than an active blockage.