Why does my aircon keep shutting off by itself?

One common cause is the float switch tripping because the drain is blocked and the pan is full. The unit shuts itself down to prevent overflow. A drain flush usually resolves this. See also the aircon-turns-off-by-itself article for other causes.

Can I clear the drain myself?

You can try blowing through the drain line from the indoor unit end with a wet-dry vacuum or by mouth. This sometimes clears light blockages. For heavy or biological blockages, a technician with a drain flush kit is more reliable.

Why does the drain keep blocking?

Algae and mould grow in the drain line when servicing intervals are too long. Regular servicing — which includes a drain flush — prevents this. If the drain blocks repeatedly between services, the service interval may need to be shortened.

Is a dripping aircon urgent?

It depends on where the water is going. Water dripping onto electrical fittings, ceiling panels, or timber flooring needs immediate attention. Water into a tray or bucket can wait for a scheduled visit as long as the unit is turned off.

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.

What You're Likely Seeing

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

What Else Causes This

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 A Proper Diagnosis Works

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 The Checks Usually Show

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.

What The Checks Usually Show summary table
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

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When This Can 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.

When To Stop Waiting

The signal is water pooling in the drain pan despite the float switch being present.

Float switch failure prevents the protection system from shutting down on overflow.

Without a working float switch, water can back up into the unit.

When water reaches dangerous levels before shutdown, float switch replacement is needed.

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.

Common questions

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