Is that ceiling stain your aircon, a hidden pipe or the slab? A practical four-clue diagnosis — location, timing, water and the meter test — with honest fix costs from a Klang Valley contractor.
Contain first, diagnose second. Put a pail under any active drip, move electronics out of the zone, and if the water is near a ceiling light or fan, switch off that lighting circuit at the DB box until things are dry. Then gather evidence while the leak is live, because an active drip is far easier to diagnose than a dry stain: photograph the stain and drip with timestamps, catch some of the water in a clean container so you can judge its colour and smell, and write down exactly what was running at the time — your aircon, the upstairs unit's aircon, the upstairs shower, or a rainstorm. Those four facts, plus a photo, are usually enough for us to identify the source over WhatsApp before anyone climbs a ladder.
Almost every ceiling drip in a Klang Valley condo or landed home traces back to one of three sources. Aircon condensate is the most common and the cheapest to fix: every running aircon produces litres of condensate a day, and when the drain line clogs with slime and dust, the tray overflows into the ceiling — yours if the fan-coil or trunking runs above, the upstairs unit's if their unit sits over your ceiling. A concealed pipe — a pressurised supply pipe or a waste pipe serving an upstairs fixture — leaks through joints or pinholes. Slab seepage is water from an upstairs wet area (usually the bathroom) working through failed waterproofing and the concrete slab. Top-floor units add a fourth suspect, the roof — if your drip tracks rainstorms rather than appliances, start with our roof leak in heavy rain guide instead.
Position is the fastest filter. A stain directly below a fan-coil unit, or running in a line along the boxed-up trunking that carries the refrigerant and drain pipes, points at aircon condensate — the drip often emerges at the trunking's lowest elbow or at a downlight along its route. A stain under the upstairs unit's bathroom, shower area or kitchen sink zone points at slab seepage; in stacked condo layouts your bathroom ceiling sits under their bathroom floor, which is why bathroom ceilings are the classic victim. A stain in a straight line that matches no trunking and no wet area above may be tracing a concealed pipe run. And a patch at the ceiling's edge against an external wall, especially below a window head, suggests rain seepage through the facade — see our external wall seepage guide for that branch of the tree.
Each source runs on a different clock, so a two- or three-day diary is the highest-value diagnostic you can do for free. Aircon condensate follows compressor hours: the drip appears after the aircon has run for a while — classically overnight — and dries up on days it stays off. Slab seepage follows upstairs water usage, appearing 10–30 minutes after their morning and evening showers. A pressurised pipe follows nothing: it drips steadily around the clock because the pipe is always under mains pressure. Rain leaks follow the weather with a lag of minutes to hours.
| When the ceiling drips | Most likely source |
|---|---|
| After your aircon has run for hours (worst overnight) | Your aircon's condensate drain |
| When the upstairs unit's aircon runs | Their condensate tray or drain line |
| 10 – 30 minutes after the upstairs shower | Upstairs bathroom waterproofing — see our upstairs bathroom leak guide |
| Constant, day and night, steady rate | Pressurised concealed supply pipe |
| Only when a specific upstairs fixture is used (toilet flush, sink) | Waste pipe joint serving that fixture |
| During or shortly after heavy rain | Roof or external facade |
Catch the drip in a clean container and look at it. Aircon condensate is essentially distilled water: clear, cool, odourless — though it may pick up grey slime from a dirty drain line. Supply-pipe water is also clean and odourless (it is your drinking water), so colour alone cannot separate those two — timing and the meter test do. Slab seepage tells on itself: it filters through concrete and old screed, arriving with a stale, musty or faintly soapy smell, leaving a brown or coffee-coloured ring on the ceiling and often a white powdery deposit (efflorescence — lime salts carried out of the slab). Waste-pipe water is the unmistakable one: grey or discoloured with a foul or soapy odour, appearing only when the fixture above is used. Persistent mould around the stain suggests a slow, long-running source — typically seepage or a weeping pipe rather than a fresh aircon overflow.
One five-minute test cleanly rules a pressurised pipe in or out. Close every tap and water-using appliance in the unit whose pipes are suspected (for a leak above your ceiling, that is usually the upstairs unit — ask nicely), then read the water meter precisely, including the small dials. Wait one to two hours with nothing used, and read it again. If the meter has advanced, water is escaping somewhere under pressure — a live supply-pipe leak. If the meter holds still, the supply pipes are tight, and your remaining suspects are condensate, waste pipes and slab seepage. One caveat: the meter test only sees the pressurised supply side. A leaking waste pipe passes the meter test because waste lines only carry water when a fixture is used — that is what the fixture-by-fixture timing in clue 2 is for.
Put the four clues together and the picture usually resolves in one pass.
| Clue | Aircon condensate | Concealed pipe | Slab seepage |
|---|---|---|---|
| Stain location | Below fan-coil unit or along trunking route | Straight line along a pipe run | Below the upstairs bathroom / wet area |
| Drip timing | After aircon runtime; stops when off | Constant (supply) or per-fixture (waste) | 10–30 min after upstairs showers |
| Water character | Clear, cool, odourless | Clean (supply) or foul (waste) | Musty, brown ring, white efflorescence |
| Meter test | No movement | Moves (supply pipe only) | No movement |
| Typical fix | Clear drain line / chemical wash | Trace, then repair or re-route the pipe | PU injection or upstairs re-waterproofing |
| Indicative cost | RM130 – RM280 | RM300 – RM1,500+ | RM650 flat (injection) |
(Indicative 2026, Klang Valley.) If your symptoms straddle two columns — say, a musty stain that also tracks aircon hours — send us the photos and the diary; mixed cases are exactly where an experienced eye earns its keep.
The usual culprit is a condensate drain line clogged with biofilm and dust, backing the tray up until it overflows into the ceiling. The fix is a proper service: a chemical wash strips the coil, blower, tray and drain line back to clean metal and clear pipe — ClickBina's aircon chemical service is RM130 flat per unit, and it both stops the overflow and restores cooling performance. Lesser causes include a sagging or kinked drain hose in the trunking (re-graded during the same visit) and sweating on uninsulated pipes, which mimics a leak as fine drips along the trunking line. If the ceiling drip appears within a day or two of an aircon installation or relocation, suspect the drain grading first. For the full menu of normal-service versus chemical-wash pricing, see our aircon servicing cost guide.
A confirmed pipe leak is plumbing work, and the job has two parts: finding it and fixing it. Tracing uses the meter test, isolation valve by valve, and listening or moisture-mapping along the run to localise the leak before opening anything — good tracing is what keeps the hacking small. The repair is either a local fix at the leaking joint through a modest access opening, or, for old and pinhole-prone embedded pipes, abandoning the buried run and re-routing a new external pipe along the wall or above the ceiling — often the more durable answer for ageing blocks. Expect roughly RM300–RM800 for an accessible joint repair and RM800–RM1,500+ where access is hard or a re-route is needed (indicative 2026, Klang Valley). Beware anyone who quotes to hack first and diagnose later — that order is backwards and it shows in the bill.
If the diary and the stain point at the upstairs wet area, the water is coming through failed waterproofing and the slab itself, and no amount of aircon servicing or repainting will touch it. The fix from your side is PU injection: ports are drilled into the slab underside and a water-reactive polyurethane resin is injected to expand into and permanently seal the crack paths — RM650 flat for one bathroom ceiling with ClickBina, including a 6-Month No-Leak Warranty, done from your unit in half a day with no hacking and no need for upstairs access. The fix at source is re-waterproofing the upstairs bathroom floor, the heavier and costlier route. The full comparison, the strata (JMB / s.142) angle and the repair sequence live in our PU injection guide and upstairs bathroom leak guide.
A special case worth naming: the drip is condensate, but the machine is not yours. When the upstairs unit's fan-coil sits over your ceiling — or their condensate drain runs through the slab zone above you — their clogged tray overflows into your ceiling exactly like a slab leak, except it tracks their compressor hours instead of their showers. The evidence that persuades: your diary showing drips aligned to their aircon usage, plus clear, odourless water. The path that works: a friendly WhatsApp with the photos first, the JMB second if needed — the management office sees this pattern constantly and can arrange the inspection. The actual fix is trivially cheap (a chemical wash on their unit), which is worth saying to the neighbour early: nobody fights over RM130. Our neighbour's aircon dripping guide covers the etiquette, the strata angle and the escalation path in full.
The reason ceiling drips drag on for months is usually contractor ping-pong: the aircon technician says it is a pipe, the plumber says it is the aircon, and the ceiling keeps dripping while everyone is half right. ClickBina runs both service lines under one roof — an aircon team that does RM130 flat chemical washes and a waterproofing team that does RM650 flat PU injection with a 6-Month No-Leak Warranty — so the diagnosis is not biased towards whichever trade showed up. Send us a photo of the stain and a note on when it drips via WhatsApp, and we'll tell you honestly what it is — and if it is a plumbing job or the neighbour's machine, we'll say exactly that. Klang Valley, appointments usually within one to two days.
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