If water is dripping from your indoor aircon unit, you are not alone — it is one of the most common aircon complaints we receive across Yishun. And in this part of Singapore, there is a very specific reason why it happens so frequently. Yishun’s tropical climate, with humidity levels consistently between 80% and 84%, creates ideal conditions for a problem that many residents have never heard of: jelly bacteria growth inside aircon drain pipes. Billy Aircon Yishun specialises in diagnosing and fixing aircon water leaks same-day, across the full Yishun area from Chong Pang to Khatib.
The Yishun Factor: Why Leaks Are So Common Here
Singapore is humid everywhere, but Yishun’s position in the North Region — bordered by forested areas near Mandai and Lower Seletar Reservoir — means the ambient humidity here is among the highest in the country. When warm, moisture-laden air passes over your aircon’s cold evaporator coil, it condenses into water, just as a cold drink forms droplets on a hot day. Under normal conditions, this condensation drains away harmlessly through the drain pipe.
The problem is the drain pipe itself. In Yishun’s heat and humidity, the slow-moving moisture inside drain pipes creates the perfect environment for a jelly-like bacterial and algal growth — sometimes called biofilm or drain slime. This gel clings to the inside of the pipe, gradually narrowing the passage until condensation water can no longer drain fast enough. It backs up inside the unit, fills the drain tray, and eventually spills out of the unit into your room.
We see this in HDB flats throughout Chong Pang, Nee Soon Central, and Nee Soon East, but it also affects newer BTO units in Yishun — Vanda Breeze, Miltonia Breeze, and the Khatib corridor estates. A brand-new unit in a new BTO flat can develop a blocked drain within 12 to 18 months if it is used heavily and not serviced regularly.
All the Causes of Aircon Water Leaks
1. Clogged Drain Pipe (The Most Common Cause in Yishun)
As described above, a blocked drain pipe is responsible for the majority of aircon water leaks we fix in Yishun. The blockage is almost always biological: jelly bacteria, algae, or a combination of both, promoted by the high humidity and warm temperatures in the drain channel.
The fix involves clearing the blockage mechanically and flushing the full drain line with pressurised water or compressed nitrogen to remove all residual gel. We also clean the drain tray inside the unit. Drain pipe flushing is included in every leak repair where drainage is the cause.
2. Dirty Evaporator Coil Causing Overflow
When the evaporator coil is coated with dust, grime, or biological growth, it cannot transfer heat efficiently. In some cases, condensation forms unevenly and runs off the coil in places it should not — bypassing the drain tray entirely and dripping directly into the room. A chemical wash of the coil resolves this and also reduces the unit’s running costs by restoring heat exchange efficiency.
For Yishun flats in taller HDB blocks — particularly those facing Yishun Ave 2 or near Chong Pang Market — coils tend to accumulate dust more quickly due to ground-level activity and cooking fumes. Annual servicing makes a significant difference.
3. Low Refrigerant Gas Leading to Ice Formation
When refrigerant levels drop below the correct charge, the evaporator coil gets too cold and ice begins to form on its surface. The unit may still appear to operate — cooling the room — but a layer of ice is building up on the coil. Eventually, the ice melts faster than the drain can handle, causing a sudden and often heavy water leak.
This type of leak is sometimes misidentified as a drain problem because the water volume is large. However, the root cause is the refrigerant shortage. Checking the refrigerant pressure at the outdoor unit is the key diagnostic step. If low gas is confirmed, we top up the refrigerant (R32 or R410A depending on your system) and check for leaks at the connection joints.
4. Improper Installation or Incorrect Pipe Slope
The drain pipe must be installed with a consistent downward slope from the indoor unit to the discharge point. If the pipe sags, has been re-routed incorrectly, or was installed without sufficient slope, water pools in low sections rather than draining freely. This is more common in Yishun’s older HDB blocks, where pipes have been modified during renovation, or in units where the aircon was installed by an unlicensed contractor.
We inspect the full drainage path — not just the pipe at the indoor unit — to identify any sagging or routing issues.
5. Cracked or Disconnected Drain Pan
The drain pan (also called the drip tray) sits beneath the evaporator coil and collects condensation before it drains away. If the pan develops a crack — from age, physical impact during servicing, or thermal stress — water bypasses the drainage system entirely. A cracked pan in an older Yishun unit is not always immediately obvious; sometimes water only appears at certain angles or load levels.
We inspect the drain pan visually during every leak diagnosis. In some cases the pan can be sealed; in others, replacement is the more reliable long-term fix.
Why You Should Not Ignore an Aircon Leak
A small drip that looks harmless can cause significant damage if left alone. Water seeping into the wall cavity behind your aircon causes long-term structural moisture damage. In HDB flats in Chong Pang, Nee Soon South, or Springleaf, a persistent leak can stain ceilings and walls, warp laminate flooring, and create the mould growth conditions that Singapore’s Building and Construction Authority warns against.
If your unit is mounted above an electrical socket or near a light switch — as many HDB bedroom units are — water tracking down the wall toward those fittings is a genuine electrical hazard. A repair that costs $50 to $120 today prevents damage that could cost thousands in renovation work and poses no risk to your family.
Our Leak Repair Process
When we arrive at your Yishun home, we work through a structured diagnostic sequence:
- Visual inspection of the unit and surrounding wall for water staining, biofilm, or physical damage.
- Drain pipe assessment — we check flow by pouring water into the tray and observing drainage speed.
- Refrigerant pressure check at the outdoor unit to rule out low gas and icing.
- Coil and drain pan inspection for fouling, cracks, or overflow conditions.
- Installation check — we trace the drain pipe routing to identify any slope or connection issues.
Once the cause is confirmed, we give you a clear price before doing any work. If multiple issues are found (for example, a blocked drain and a dirty coil), we explain each one and let you decide how to proceed.
All leak repairs come with a 90-day warranty. If the leak returns within 90 days due to the same cause, we come back at no charge.
Covering All of Yishun
We serve the full Yishun area: Chong Pang, Nee Soon Central, Nee Soon East, Nee Soon South, Springleaf, Lower Seletar, Khatib, and all BTO developments in the area. We also cover nearby towns accessible via the SLE and TPE — including Sembawang, Canberra, Woodlands, and Mandai — so if you are just outside the Yishun boundary, get in touch and we will confirm.
Stop putting a bucket under your aircon. Call Billy Aircon Yishun and get it properly fixed today.
