Older HDB Trunking Drip: Cracked Drain Elbow Behind Casing

Clearing the drain keeps not working on an older flat. When repeated clearing fails, the fault is not the blockage anybody keeps removing.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

How this presents

Water forming below the trunking, returning whenever the unit runs more than an hour. The drain has been flushed once already and the leak came back. The indoor tray is not overflowing, which is the detail that does not fit a blocked line.

Setup: Mitsubishi Electric Wall-mounted4-6 yearsHDBHougang
Misread as: The indoor unit needing replacement, because clearing the drain kept not working.
Check first: Where the water mark starts, once the tray is confirmed not overflowing

What else produces this

A choke and a breach produce the same puddle and behave completely differently. A choked line backs water up until the tray overflows, so the tray is the evidence. A breach lets the tray drain perfectly and loses water somewhere downstream instead. A tray that is not overflowing rules out the first, which turns the job from flushing into tracing.

An indoor tray draining normally, not overflowing, rules out a blockage upstream of it.
A water mark beginning at a bend, rather than at the unit, locates the escape instead of the drip.
A cracked elbow found at that bend explains the whole pattern with nothing else needed.
A pipe run clear after the elbow keeps the repair to one section instead of the full route.

Why it happens

Plastic ages and a bend carries the stress, so an elbow is where a run cracks first. Water leaves the tray correctly, travels the hose, and escapes at the crack into the trunking, which then acts as a channel. It runs along the inside until it finds a low point and drips out there. The visible drip is downhill of the fault, sometimes well downhill, and the trunking decides where.

What resolution involves

Replace the cracked section and seal the joint, then run water through the tray while watching both the opened bend and the trunking exit. Watching only one of the two is how a partial repair ships. The run past the elbow stays, because it passed a flush and there is nothing to gain from replacing pipe that works. A full re-run is for a route failing along its length, not at one bend.

How to tell it worked

Both ends watched during the water test: the bend that was opened, and the point the drip came from. A repair confirmed only at the repair is confirmed at the wrong end.

Before you approve a quote

The drip is downhill of the fault, not at it

A tray that is not overflowing rules out a blocked line. Flushing again proves the route carries water, not that it holds it.
Follow the water mark to where it starts, and open that section first.
Inside a covered run, water travels before it drips. The visible wet patch is not the fault.

Questions this case answers

Water is dripping from the trunking, not from the aircon itself. What does that mean?

Usually that water is escaping partway along the run rather than backing up at the unit. A breach lets the tray drain perfectly and loses water downstream, where the trunking channels it along until it finds a low point. The drip is where gravity released it, not where the pipe failed.

Why did the drip come back after the drain was flushed?

Because flushing addresses a blockage, and a blockage was never the fault. A flush proves the route can carry water. Whether the route holds water is a different question, and it is the one a crack asks.

Do I need a new indoor unit if the drain keeps leaking?

Not on this pattern. A tray draining normally means the indoor unit is doing its job, and the fault sits in the pipework beyond it. Replacing the unit would leave the cracked section exactly where it is.

Which section of trunking should be opened first?

The section where the water mark begins, not the section where it drips. Following the stain back to its highest point puts the opening at the escape rather than downstream of it, and usually keeps the repair to one bend.

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