BTO bedroom leaking at trunking: drain pipe pinched behind a shelf

A Sengkang BTO bedroom started leaking from the trunking though the flat was not old. The drain line looked untouched, but a shelf fitted during a past renovation had pinched the pipe behind the wall. The question was whether the water was blocked, backflowing, or escaping through a narrowed section.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Daikin Wall-mounted4 years oldHDBSengkang, Singapore

Concern: The owner expected another drain flush, but the leak kept returning after short-term clearing.
Found: A section of trunking pinched behind a shelf added during a past renovation, narrowing the drain pipe's bore
Key check: Checked the trunking route for a narrowed section behind fixtures before recommending cleaning alone
Result: The wet patch did not return after a full overnight run. The bedroom had a point-specific fix instead of another temporary drain clearing.

What we were told

The bedroom unit leaked near the trunking after running through the night. A previous drain clearing had helped briefly, but the same wet patch came back. The flat was relatively new, so a route issue seemed unlikely. That made the repeated pattern more important than the age of the flat.

What we checked

Repeat leakage after a short-term flush made us trace the trunking route rather than just clear the pipe opening. Water passed through fine at low flow, which pointed away from a blockage. We looked for a physical restriction along the run and found a section running behind a built-in shelf added after the original installation.

Water could pass through the drain fine when tested at a normal, steady flow.
A section of trunking behind a built-in shelf showed the pipe pressed noticeably out of round.
The first wet point matched that pinched section, not any low spot in the route.
The indoor pan was not cracked and the coil was not icing.

What we found

A shelf added during a past renovation had been fixed to the wall directly over the drain trunking, and its bracket pressed the pipe out of round at one point. That narrowed section still passed water at normal, steady flow, so the drain worked fine on an ordinary day. Overnight runs push more condensate through the line in one stretch, and once that higher volume reached the narrowed point, it could not clear fast enough and backed up toward the trunking seam. The pipe itself had not sagged and had no low point; the restriction was a pinch, not a dip, and only showed up under heavier flow.

What fixed it

We freed the trunking from the shelf bracket and rerouted that short section clear of the pinch point, restoring the pipe's full bore. We explained that re-levelling a sag would not have helped here, since the pipe was never sagging. The homeowner was shown exactly where the shelf had pressed against the trunking, since the fixture being newer did not rule out an installation-era conflict. The practical fix was relieving that one section, not repeated flushing or route re-levelling.

Outcome

The wet patch did not return after a full overnight run. The bedroom had a point-specific fix instead of another temporary drain clearing.

What this case teaches us

Newer flats can leak from a pinched pipe, not just a drain choke

A drain can pass water fine under normal use and still fail when a section is pinched narrow. Renovation fixtures fixed near trunking are worth checking.
Long trunking runs in newer flats should be checked for physical pinch points, not just sagging. This matters most when a leak only shows up after heavier overnight use.
Ask whether the drain route was traced for crushed or narrowed sections, not only whether water was pushed through the pipe.

Questions this case answers

Drain was cleared but the bedroom leak keeps coming back. What is being missed?

A physical restriction rather than a blockage. In this Sengkang flat water passed through fine at a normal steady flow, which is why flushing seemed to work each time. A section of trunking behind a built-in shelf showed the pipe pressed noticeably out of round, and the first wet point matched that spot.

Can a newer flat have a drain problem this soon?

Age was not the factor. A shelf added during a past renovation had been fixed to the wall directly over the drain trunking, and its bracket squeezed the pipe out of round. The flat being relatively new made the owner discount a route issue, when the fixture itself was the conflict.

Leak turns up only after the aircon runs all night. What causes that?

Volume. Overnight cooling pushes far more condensate through the line in one stretch than an ordinary evening does, and once that flow reached the narrowed point it could not clear fast enough and backed up toward the trunking seam. Anything shorter passed through the pinch without trouble.

Is re-levelling the drain pipe the usual fix for a repeat leak?

Only when the pipe is actually sagging. This one had no low point at all, so re-levelling would have changed nothing. Freeing the trunking from the shelf bracket and rerouting that short section restored the pipe's full bore. Ask whether the route was traced for crushed or narrowed sections, not only whether water was pushed through.

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