Older HDB trunking drip: cracked drain elbow behind the casing

Mitsubishi Electric Wall-mounted·13 years old·HDB·Hougang, Singapore

Water kept forming below the trunking. The drain had been flushed once before, but the leak returned whenever the bedroom unit ran for more than an hour.

The indoor tray was draining at first, so we followed the water mark along the trunking rather than treating it as a simple choke. Repeated flushing would only prove that water could move through part of the route. It would not prove that the route was still watertight at the bend where the mark began. We opened the section around the first stain before touching the rest of the run, so the check stayed focused on where water first escaped.

The plastic drain elbow had aged and cracked at the bend. Water entered the drain hose, then escaped at the cracked elbow and ran along the inside of the trunking before dripping out lower down. A cracked elbow behaves differently from a choke. Water can still leave the tray, so the indoor unit may not overflow. But once the water reaches the damaged bend, some escapes into the trunking and travels until it finds a low point to drip out. That is why the visible drip was lower than the actual fault. The water was following the trunking path, not falling straight from the break.

We replaced the cracked elbow section, sealed the joint, and ran water through the drain tray to confirm the trunking stayed dry. We kept the repair to the damaged section because the rest of the run passed the flush test. After replacement, we watched both the opened bend and the lower trunking exit during the water test. That kept the repair limited to the visible failure point while still proving the drain could carry water after the joint was replaced. The customer did not need a full re-run because the pipe after the elbow moved water cleanly once the crack was removed.