Water Marks on Ceiling: Drain Pump Switch Stuck by Sludge

Water marks appear on a ceiling under a ducted system. Whether the pump broke down or was simply never asked to run.

By Team Snowflake | Updated 24 Aug 2026

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

How this presents

Water overflowing from a concealed unit while the pump itself appears entirely sound. Power is present and the pump runs when it is energised directly. The overflow happens whenever the unit runs for any length of time.

Setup: Daikin Ducted7-9 yearsLandedTanglin
Misread as: A pump at fault on a system that is hard to reach, with disruption involved in getting at it.
Check first: Whether the pump starts by itself as the pan fills, rather than when energised by hand

What else produces this

A pump that runs when energised directly has already answered the question about itself. What has not been tested is whether anything ever energises it in normal operation, and that is the switch's job. A level switch reports water rising and is what closes the circuit. One held in its low position never reports anything, so the pump waits, correctly, for a call that never comes.

A pump running normally when energised directly removes the motor and the supply from the search.
No response from the pump as the pan fills up shows that nothing is closing the circuit for it.
A level switch held down by deposit cannot report the rising water it sits in.
The same switch moving freely once cleaned confirms it as the only element that had actually failed.

Why it happens

A level switch floats on the water it is measuring, which means it sits in the same deposit the pan collects. Sludge around its travel holds it down, and a switch that cannot rise cannot close its circuit. Everything else in the chain remains sound and idle. That is what makes this fault so easy to misdiagnose as a dead pump when only the pump itself gets tested.

What resolution involves

The switch and its chamber are cleaned so it moves freely again, and no part is replaced. The general habit is worth more than the repair: test the sensing element and the acting element separately, because a chain reports as broken wherever it is opened. A pump tested in isolation proves only that the pump works.

How to tell it worked

The pan filled with water and the pump watched starting by itself, rather than being energised by hand. Only an unassisted start proves the switch is doing its own part of the job properly.

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Test what asks separately from what acts

A pump that runs when energised directly proves the pump, and nothing at all about the switch.
A level switch sits in the deposit it is measuring. Sludge holds it down and it stops reporting.
Fill the pan and watch for an unassisted start. That is the only test covering the whole chain.

Questions this case answers

Water marks on the ceiling under a ducted unit: does the pump need replacing?

Usually not. A pump that runs when energised directly is working, and the fault here was the level switch held down by sludge. Cleaning the switch and its chamber restored the chain with no part replaced.

The pump runs on the test button, so why is water still overflowing?

Because the level switch floats on the water in the pan, so it collects the same sludge the pan does. Deposit around its travel holds it down, and a switch that cannot rise never closes the circuit to call the pump.

What is sludge doing inside a drain pump reservoir?

It settles around the level switch's travel and holds it down, so the switch cannot rise and never reports the rising water. The pump is never called even though it is sound, and cleaning the switch and its chamber restores free movement.

Can this be fixed without opening the ceiling?

In this case yes: the fault was a sludge-held switch and the repair was cleaning rather than replacement, with no new pump fitted. Fill the pan with water and watch, and the pump should start on its own and stop once the pan is clear.

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