Concealed unit dripping from the panel: drain pump seized

Water dripping from two points on a ceiling unit panel looks like a serious leak. Often it is the opposite. Here the drain pump had seized, so condensate backed up through the tray with nowhere to drain.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Mitsubishi Electric Ceiling-concealed7 years oldCondoNovena, Singapore

Concern: A refrigerant leak, or structural damage behind the dripping, was the first reading.
Found: drain pump seized from scale and algae buildup inside the chamber
Key check: Access panel opened, tray found overflowing, pump shaft would not turn
Result: The dripping stopped as soon as the pump was replaced. We advised adding a pump chamber flush to the yearly service, a step many skip on concealed units because it means opening the panel.

What we were told

Water had started dripping from the unit panel two days earlier. It was small at first but kept getting worse. The owner worried about water damage and suspected a refrigerant leak.

What we checked

We opened the access panel and checked the tray, drain line, and pump in turn. On a concealed unit the source has to be narrowed down step by step, because the tray, pump, drain line, and a frosted coil each leak in a different way. A drainage fault is far more common than a coil leak. A quick gas check tells the two apart in minutes.

The drain tray was overflowing. Water sat above the tray lip and seeped through panel joints at two points along the front edge.
The drain pipe from tray to pump inlet was clear, with no blockage or pinch in the line.
The pump had power at the connections, but the shaft would not turn. The motor hummed without rotating.
Inside the pump chamber, heavy scale and algae had built up around the impeller and locked it against the chamber wall.
Gas readings at the service port were normal, which ruled out a coil leak as the water source.

What we found

Over seven years, mineral scale and algae built up inside the warm, damp pump chamber and coated the impeller and chamber walls. That buildup slowly added friction, so the pump likely weakened over months before it seized. Once the impeller locked, drain water had no way out. It filled the tray faster than it could evaporate, rose above the lip, and seeped through the panel joints. The drips looked like they came from several places because the water spread across the top of the panel before finding gaps. The refrigerant circuit and coils were fine. This was a drainage failure from a pump chamber that had never been cleaned.

What fixed it

We removed the seized pump and fitted a matched replacement rated for the same lift height and flow. The tray was cleaned, dried, and checked for cracks from the long water contact. We flushed the drain pipe from tray to pump inlet to clear any sludge. After priming the new pump, we filled the reservoir by hand to confirm it switched on at the right water level and drained fully. We then cycled the system fully and confirmed the tray stayed dry before closing the panel.

Outcome

The dripping stopped as soon as the pump was replaced. We advised adding a pump chamber flush to the yearly service, a step many skip on concealed units because it means opening the panel.

What this case teaches us

A dripping ceiling unit usually means a blocked drain, not a leak

On a concealed unit, drips from several spots often trace back to one cause: water backing up in the tray.
The drain pump on a ceiling unit can seize from scale and algae. A yearly flush of the pump chamber prevents it.
A quick gas check rules out a refrigerant leak in minutes, so the fault gets found faster.

Questions this case answers

Water dripping from a ceiling aircon panel: is it a refrigerant leak?

Drainage is the far more likely answer, and a gas check settles it quickly. On this Novena concealed unit the readings at the service port were normal, which ruled the refrigerant circuit out early. The tray was overflowing instead, with water sitting above the lip and finding its way out through the panel joints.

Why does the water seem to come from several places at once?

Because it spreads before it escapes. Once the tray overflows, water runs across the top of the panel and drips wherever it finds a gap, so one fault looks like several. Two drip points on this unit traced back to a single cause. Chasing each drip separately wastes time; finding why the tray is full does not.

What makes a condensate pump stop working?

Scale and algae building up inside a warm, damp chamber. That coating adds friction to the impeller until it locks against the chamber wall. The pump here had power at its connections and hummed without turning, which is the signature of a seized impeller rather than a dead motor or a wiring fault. Drain water then had nowhere to go.

Is a seized drain pump worth cleaning instead of replacing?

Not reliably, once buildup has locked the impeller hard against a scaled chamber. A matched replacement rated for the same lift and flow went in here, the tray was cleaned and checked for cracks, and the pipe from tray to pump inlet was flushed. Adding a pump chamber flush to the yearly service is what stops the buildup returning.

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