Aircon Ceiling Unit Overflow

Case Details

What We Checked

• Drain line had flow when pump was manually triggered — confirming the pipe was not blocked.
• Pump motor itself could run and sounded healthy under forced activation.
• Float movement was not smooth through full travel — it stuck at a midpoint and needed a nudge to continue rising.
• Tray level rose 15–20mm above the normal trigger point before the pump finally engaged.
• A film of sludge and biological growth was visible on the float shaft and inside the chamber walls.

The Diagnosis

Sludge and biological growth had accumulated inside the condensate pump chamber over years of operation, coating the float shaft and restricting its vertical travel. When condensate entered the tray, the float could not rise freely to its trigger point — it stuck partway up, delaying the pump activation signal. Condensate continued to accumulate during this delay, and on longer cooling cycles where humidity load was high, the tray level exceeded its capacity and overflowed before the pump finally engaged. The overflow was intermittent because shorter cycles or lower-humidity periods did not always push the tray level past its limit — the float would eventually unstick and catch up. This made the leak appear random, and because the pump could still run when manually triggered, previous checks had cleared it as healthy.

What Fixed It

We explained that the pump motor and drain line were both healthy — the only issue was the float mechanism inside the pump chamber. We cleaned the float shaft, chamber walls, and intake screen to restore full float travel, then ran the system for an extended cycle to verify that the pump engaged consistently at the correct tray level. We also checked the discharge line for any partial restriction that could slow drainage. No pipe replacement or pump swap was required — the entire fix was a targeted clean and restore of the float mechanism.

Overflow stopped after float restoration. Discharge remained stable through repeated run checks.

Why This Happens

Why intermittent ceiling leaks are often switch-timing faults.

• On-and-off leaks often point to control behavior, not a blocked pipe. A consistent blockage produces a steady leak, but a sticking float creates a pattern that comes and goes with run duration and humidity load.
• A pump can run when forced but still fail in normal cycles if the float sticks. Manual testing alone does not prove the pump is healthy — you need to watch its response under real condensate load over several minutes.
• Live tray-level and float-movement checks are the only reliable way to confirm this pattern. Watching the water level rise and timing how long the float takes to trigger the pump reveals the delay that causes overflow.
• Debris buildup inside the pump chamber is gradual. Sludge, dust, and biological growth coat the float shaft and restrict its travel, so the problem worsens slowly — often unnoticed until ceiling stains appear.