Cassette dripping onto desks: drain sludge, not a cracked pan
Water dripped from the cassette unit onto the desks below. A previous assessment said the drain pan had cracked. From the floor, a cracked pan and a blocked drain look the same. The question is whether water leaks through the pan or spills over its edge.
By Team Snowflake | Reviewed 10 Mar 2026
Case summary
Daikin Cassette14 years oldIndustrialChoa Chu Kang, Singapore
- Concern
- Previous advice was that the drain pan had cracked, so the cassette had to be lowered from its ceiling mount for a pan replacement.
- Found
- Drain line fully blocked with sludge causing water to back up into the pan and overflow, pan itself intact
- Key check
- Flushed drain line and inspected pan surface before condemning the pan
- Result
- The leak stopped the moment the drain line was flushed. The cassette kept running on its original drain pan, with no ceiling work or unit removal.
What we were told
Water has been dripping from the indoor unit onto the desks below. Another company said the drain pan had cracked from age, so the unit had to be lowered from the ceiling for a pan replacement. The unit is old, so full replacement was also on the table.
What we checked
Before assuming the pan had cracked, we checked the drain line. We poured a small amount of water into the pan to see whether it left through the outlet. Nothing came out, which pointed to a blockage. We then went over the pan surface for cracks or corrosion. A cracked pan leaks through its surface, while a blocked drain backs up and overflows the edge.
The drain line was completely blocked with thick sludge. No water flowed out of the drain.
Drain water was backing up inside the pan and spilling over its lowest edge.
After the drain line was flushed clear, water drained freely and the overflow stopped at once.
The pan surface showed no cracks, fractures, or corrosion. The pan body was sound.
What we found
The drain line had slowly blocked with sludge, a mix of algae, bacteria, and dust that builds up over years of use. In a ceiling-mounted cassette, the drain line runs flat before a vertical drop, and sludge gathers along that flat run where water moves slowest. Once it blocked fully, the water backed up in the pan and spilled over the edge onto the desks below. It was going over the pan, not through it. The previous contractor saw the dripping and decided the pan had cracked, but never checked the drain line.
What fixed it
We flushed the drain line with pressurised water until the sludge cleared and water ran freely, then poured test water into the pan to confirm drainage was restored. No ceiling work was needed, no parts were replaced, and the unit stayed on its mounting. We advised adding a drain flush to every service. On a cassette running long office hours, that is the best way to prevent a repeat leak.
Outcome
The leak stopped the moment the drain line was flushed. The cassette kept running on its original drain pan, with no ceiling work or unit removal.
What this case teaches us
A dripping cassette is usually a blocked drain, not a cracked pan
- Pour a little water into the pan and watch the drain outlet. If nothing comes out, the line is blocked and the pan may be fine.
- Overflow spills at the pan edge, a cracked pan leaks through its surface. Which one it is decides between a quick flush and a costly teardown.
- On a cassette running long office hours, add a drain flush to every service. It is the cheapest way to stop a repeat leak.
Related reading
Ready to get started?
Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.