Why is my Panasonic aircon leaking water after long runs?
A Panasonic drip that arrives after hours of cooling, and never after a short run, is telling you something. The drain has not closed. It is passing water more slowly than the coil is filling the tray.
By Team Snowflake | Updated 18 Aug 2026
A slow drain leaks differently from a blocked one
A fully blocked drain floods within the hour, every time the unit runs. A timed drip does not behave like that. Water still leaves the tray. It just leaves more slowly than the coil fills it.
That is a race between two rates, and the tray is the buffer sitting between them. On a short run the drain keeps up. On a long run the level climbs past the lip and spills over.
This is why the unit still cools while it drips. It is also why the leak feels random, and why a quick on-off test in front of a technician shows nothing wrong at all.
Time the drip against the run
Note the run length before the first drop, then match it below. Timing does more work here than the spot the water lands on.
A leak that takes hours to appear is a restriction rather than a break, and the length of the run says how far down the route it sits.
A leak that only follows a full night, with the water tracking along the trunking instead of the unit, is often not drain water at all.
There is also a stage before the drip. A pan that drains too slowly holds water between cycles, and the room smells musty at start-up while the cooling stays fine. Nothing has overflowed yet. The line is already narrowing, and flushing it then is cheaper than flushing it after a ceiling stains.
| What the leak does | Most likely cause | Where to look first |
|---|---|---|
| What the leak doesAppears after several hours, every time | Most likely causeSludge narrowing the line further down the run | Where to look firstThe hidden section behind the trunking |
| What the leak doesSame hour each afternoon under steady load | Most likely causeA partial blockage that peak load outruns | Where to look firstThe pipe run, not the trap |
| What the leak doesOnly after a full night, water on the trunking | Most likely causeA cold pipe sweating through a gap in its insulation | Where to look firstInside the cover at the wet section |
| What the leak doesReturns soon after the line was cleared | Most likely causeA dip or reverse slope holding water in the route | Where to look firstThe fall of the pipe along its full length |
| What the leak doesStarted within weeks of renovation work | Most likely causeFine dust set into a choke in the drain path | Where to look firstThe drain path nearest the unit |
| What the leak doesNo drip yet, but a musty smell at start-up | Most likely causeA pan draining too slowly to empty between cycles | Where to look firstThe pan, and how fast it empties |
Water on the trunking is often not drain water
Trunking carries cold pipe, drain pipe and cable inside one cover. Two of those can wet a wall, so a damp seam settles nothing on its own.
The common one is sweat. Where insulation on the cold pipe has opened up, humid room air reaches bare metal and condenses on it. That water collects inside the cover and tracks down until it finds a seam.
Sweat has a signature. It needs a long cold soak to form, so it follows a full night and never a short session. The mark also starts away from the unit casing, at the point where the gap sits.
Drain water behaves differently. It backs up first, then escapes at a joint or a low point, and it follows cooling load rather than pure runtime. Opening the cover at the wet section separates the two in a minute. That should happen before anyone quotes a new drain line.
The distinction decides the repair. Fit a new drain line to cure a sweating pipe and the damp patch survives the work, along with the bill. Sealing the insulation, then rechecking the drain before the cover goes back, is the proportionate job.
When a clearing does not hold
A leak that returns after the line was flushed is usually about the shape of the route, not what is sitting inside it.
Flushing removes debris and leaves the geometry untouched. A section sloping the wrong way holds water however clean the pipe is, and it fills again on the next long run.
Reverse slope turns up most in retrofitted trunking. A drain fitted around an existing building takes awkward turns, and one of them ends up level or falling backwards. Long runs, tight bends and flat stretches all raise the odds.
The same rule governs a new installation. Condensate moves only while the pipe keeps falling, the whole way, with no exceptions anywhere along it. A beam overhead costs the line its fall. Recovering that fall elsewhere is harder than routing around the beam, so the route gets levelled end to end before the ceiling closes.
Telling dirt from slope
Count the clearings. One that held for years points at dirt. A drip back soon after the last flush points at the route.
Watch the line after shutdown. Water that seeps out once the unit stops has been sitting in a low point. A clean pipe with proper fall empties itself and stays quiet.
Before anyone opens the unit
Photograph the mark before wiping it. Where a stain starts, not where it ends, shows a technician which section gave way.
Kill power at the isolator if the water is tracking toward a light fitting, a socket, or a void above a ceiling. Nothing else here is urgent. Condensate is room moisture, not refrigerant, and it forms on the outside of sealed pipework.
Then keep it switched off. More cooling means more water arriving at a route that already cannot clear it, and a larger stain to explain later.
Question any quote that opens with a tray, a coil or a full drain replacement. A flow test along the whole route, under a real cooling load, takes minutes and is what shows whether those parts are involved at all.
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Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.