HDB wall unit dripping traced to algae-choked drain tray
Aircon case in Balestier, Singapore: water leakage traced to drain tray choked with algae and biofilm blocking the drain outlet, causing condensate to overflow the tray and drip from the front of the unit after targeted diagnosis checks.
Case details
What client reported
Water has been dripping from the front of the wall unit onto the parquet floor in the master bedroom. The client placed towels under the unit but the drip was getting worse. They were worried the drain tray had cracked and the unit would need major disassembly or replacement.
What we found
A front-facing drip on a wall unit points to the drain tray overflowing rather than a pipe leak at the back. We opened the unit to inspect the tray before testing anything else.
- Drain tray had a thick layer of green algae and biofilm covering the entire tray surface and blocking the drain outlet
- Condensate was pooling in the tray with no path to the drain line — water was spilling over the front edge
- After cleaning the tray and clearing the outlet, water drained freely into the drain line
- Tray surface was inspected after cleaning — no cracks, holes, or corrosion found
Algae and biofilm had built up in the drain tray over several years of use. The growth gradually covered the drain outlet until water could no longer flow out. Condensate backed up in the tray and overflowed from the front of the unit. The tray itself was structurally intact.
What we did
GOOD NEWS — the drain tray was not cracked. The drip was caused by algae blocking the drain outlet. We cleaned the tray, cleared the biofilm from the outlet, and flushed the drain line to confirm flow. No parts were needed.
The drip stopped immediately after the tray was cleaned and the drain outlet cleared. The unit resumed normal operation with its original drain tray. The parquet floor was dried and no lasting damage was found.
Timeline
Day 1
Wall unit dripping from the front onto parquet floor — worried about cracked tray
Day 1
Removed the front panel and inspected the drain tray surface and outlet before testing the drain line
Day 1
Algae-choked drain tray cleaned, outlet cleared — drip stopped immediately
What we learned
Why drain trays block up — and what causes algae growth.
- The drain tray sits under the evaporator coil and collects condensate. In warm, humid conditions like Singapore, the standing moisture creates an environment where algae and biofilm grow. Over time the growth covers the drain outlet and blocks water from flowing out.
- A choked drain tray overflows from the front of the unit. This looks alarming but does not mean the tray is cracked. Cleaning the tray surface and flushing the drain outlet restores normal flow.
- Regular servicing that includes drain tray cleaning prevents algae from building up to the point where it blocks the outlet. Units in bedrooms are especially prone because the tray stays damp overnight when the unit runs during sleep.
Best next step
If your unit is behaving similarly, start with the service path that fits this case before approving broader scope.
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