Aircon Concealed Unit Dripping

Case Details

What We Checked

• Condensate tray was overflowing — water sat above the tray lip and was seeping through panel joints at two points along the front edge.
• Drain pipe from tray to pump inlet was clear — no blockage or pinch in the line.
• Pump had power at the terminals but the shaft would not turn when energised — motor hummed but could not rotate.
• Pump chamber opened and inspected — heavy scale and algae deposits had built up around the impeller, locking it in place against the chamber wall.
• Refrigerant pressures spot-checked at the service port — within normal range, ruling out a coil leak as the water source.

The Diagnosis

Over seven years, mineral scale from Singapore's water supply and algae growth from the warm, damp environment inside the pump chamber had progressively coated the impeller and chamber walls. The buildup increased the friction on the impeller shaft incrementally — the pump likely slowed over months before finally seizing. Once the impeller locked, condensate had no exit path. Water accumulated in the drain tray faster than it could evaporate, rising above the tray lip and seeping through the panel joints at the lowest points. The dripping appeared to come from multiple locations because the water was spreading across the top of the panel before finding gaps. The unit's refrigerant circuit and coils were unaffected — this was purely a drainage failure caused by a neglected pump chamber.

What Fixed It

The seized pump was removed and replaced with a matched unit rated for the same lift height and flow rate. The condensate tray was cleaned, dried, and inspected for any cracks or deformation from the prolonged water contact. The drain pipe from tray to pump inlet was flushed to clear any residual sludge. The new pump was primed, and we filled the reservoir manually to confirm it activated at the correct water level and drained completely. We ran the aircon through a full cooling cycle and verified the tray stayed dry throughout before closing the access panel.

Dripping stopped straight after the pump was replaced. The client was advised to add pump chamber flushing to the annual service. It's a step some technicians skip on concealed units because it requires opening the panel.

Why This Happens

Condensate pump failure vs. blocked drain pipe.

• Wall-mounted units drain condensate by gravity and do not need a pump. Concealed and ceiling units often cannot rely on gravity because the drain outlet is above the nearest drainage point. A pump lifts the water out. If it fails, water has nowhere to go — the tray fills, overflows, and drips from every low point on the panel.
• Scale and algae build up inside the pump chamber over years because the chamber stays warm and damp — an ideal growth environment for biological growth and mineral deposition. The impeller gets progressively harder to turn until it seizes. By the time the homeowner notices dripping, the pump has usually been struggling for months, cycling sluggishly before finally locking up.
• Flushing the pump chamber with a dilute descaler once a year prevents seizure. It is far cheaper than a pump replacement — typically a fraction of the cost — and takes only a few minutes during a service visit. Ask your technician whether they include the pump chamber in their regular service scope. Many skip this step on concealed units because accessing the pump requires opening the panel, which adds time.
• Dripping from multiple points on a concealed unit panel does not necessarily mean multiple leaks. Water from an overflowing tray spreads across the top surface of the panel before finding the lowest gaps in the joints. One overflowing tray can produce drips at two or three locations, creating the misleading impression of multiple independent leak sources.