Office cassette leaked after service: pump cover left misaligned

The cassette had just been serviced, then started dripping over desks. The first check was whether the pump and cover were reassembled correctly. A leak that starts the same day as cleaning should first be checked where the cassette was opened and reassembled.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Mitsubishi Electric Cassette6 years oldOfficeStraits View, Singapore

Concern: Office manager worried the ceiling drain pipe had failed above the desks.
Found: Drain pump cover left slightly misaligned after servicing
Key check: Opened the cassette panel and checked pump cover seating before flushing the full drain line
Result: The leak stopped on the same visit. No ceiling pipe work was needed. The office avoided ceiling opening and after-hours disruption. The leak was a reassembly issue at the cassette, not a failed concealed drain. That distinction mattered because ceiling work would have been slower, messier, and unrelated to the actual fault. The same-day timing after servicing was the clue that kept the repair focused.

What we were told

The office ceiling unit was serviced in the morning and began dripping over desks later that day. It had not leaked before the service.

What we checked

The timing pointed to a service follow-up. We opened the cassette panel and checked the pump area before chasing the ceiling drain route. We recreated the drain condition while watching the pump area directly. That was more useful than flushing the ceiling line from a distance because the suspected escape point was inside the cassette. We also checked reassembled parts first, since the leak began after work rather than after weeks of slow drainage.

Pump ran when water entered the tray.
Pump cover was slightly misaligned.
Water escaped around the cover during a drain test.
The ceiling drain line after the pump was clear.

What we found

The pump cover had not seated fully after servicing. Water entered the pump chamber but escaped at the misaligned cover before being discharged into the drain line. The pump was moving water, but the cover was not seated squarely. Water found the small gap around the cover before it could be discharged cleanly. From below, that looked like a ceiling drain failure even though the fault was inside the service panel. The timing after service made reassembly the first place to prove or rule out. The ceiling route did not need to be opened because the leak appeared before water reached that part of the system.

What fixed it

We reseated the pump cover, checked the gasket, and ran water through the cassette until the pump cycled several times without dripping. We confirmed the gasket and cover position before closing the cassette because a misaligned cover can look fixed briefly, then leak again when the pump cycles. Repeating several pump cycles proved the seating was stable. We did not recommend ceiling work because the controlled water test showed the pump area stayed dry after the cover was seated correctly.

Outcome

The leak stopped on the same visit. No ceiling pipe work was needed. The office avoided ceiling opening and after-hours disruption. The leak was a reassembly issue at the cassette, not a failed concealed drain. That distinction mattered because ceiling work would have been slower, messier, and unrelated to the actual fault. The same-day timing after servicing was the clue that kept the repair focused.

What this case teaches us

Post-service cassette leaks need reassembly checked

A leak right after cleaning often starts with disturbed pump covers, drain hoses, or panel seating. Same-day leaks after servicing should start with the parts opened during servicing.
Check the cassette internals before opening ceiling routes. For cassette units, pump covers and gaskets are common reassembly points to verify.
Timing and drip location help separate reassembly faults from old drain chokes. If water is dripping over desks, note whether it began before or after cleaning; that changes the first inspection.

Questions this case answers

Ceiling cassette started dripping over desks the same day it was cleaned. Where do we look?

Inside the cassette, at whatever was opened during that clean. The pump ran when water entered the tray, but the cover above it was not seated squarely and water escaped around it. The ceiling drain line beyond the pump was clear, so nothing above the tiles needed opening.

Does water over the desks mean the ceiling pipe has failed?

It looks that way from below, and often it has not. A drip starting inside the service panel lands on the ceiling and reads as a concealed pipe problem. A controlled water test with the panel open put the escape point at the pump cover, well before water reached the ceiling route.

Can this be repaired without opening the ceiling?

It was here. Reseating the cover, checking the gasket and running water until the pump cycled several times ended the drip on the same visit. Several cycles were run because a misaligned cover can look settled briefly, then leak again. Avoiding ceiling work saved the office an after-hours disruption.

Why does the timing of the first drip matter so much?

It decides where the inspection starts. A unit that never leaked before and drips hours after cleaning puts the reassembled parts at the front of the queue, ahead of any old drain choke. Noting when the drip began and where it exits the panel kept this repair small and same-day.

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