Drips only on humid days: drain pipe sagged and water pools inside
A wall unit in an older home dripped only on humid days. The owner feared a cracked drain pipe inside the wall that would need hacking. But a crack drips at a steady rate, whatever the weather. Dripping tied to humidity points somewhere else.
By Team Snowflake | Reviewed 11 Mar 2026
Case summary
Hitachi Wall-mounted14 years oldLandedBishan, Singapore
- Concern
- Feared the drain pipe inside the wall had cracked and the wall would need hacking open to replace it.
- Found
- Drain pipe had sagged at a section along its run, creating a low point where drain water pooled and overflowed back toward the indoor unit on high-humidity days
- Key check
- Traced the full drain pipe run and checked the gradient at each support point before assuming the pipe was cracked
- Result
- The dripping stopped. The pipe now drains freely on both dry and humid days. The wall was left untouched and the original pipe stays in service.
What we were told
The living room aircon has been dripping on and off for a few months. It only happens on really humid days, and on dry days it is fine. The house is old and the pipes run through the wall. We are worried the drain pipe has cracked inside and the wall will need hacking open.
What we checked
Dripping that comes and goes with humidity means the drain copes with normal water but overflows when the volume rises. A cracked pipe leaks at a steady rate. The pattern pointed to a flow problem, not a break. We traced the full drain run from the unit to the discharge point and checked the slope at every reachable bracket.
The drain pipe had a visible sag where a support bracket had shifted off the wall, pulling the pipe into a dip.
The dip held standing water even with the unit off. About 50ml of stagnant water sat in the U-shaped low point.
On humid days the water arrived faster than it could trickle past the dip, so it backed up and overflowed from the drain pan.
The pipe at the dip showed water marks and a faint musty film, the sign of long-standing water.
After we resupported the pipe and restored the slope, water flowed freely through the whole run.
What we found
Over fourteen years, the wall anchor holding one bracket had slowly worked loose from the plaster. As it lost grip, the bracket sagged under the weight of the pipe and the water inside it, forming a U-shaped dip that acted as a trap. On normal days the unit produced water slowly enough to trickle past. On humid days output rose sharply, water backed up faster than the dip could clear, and the trapped water overflowed from the drain pan. The pipe itself was intact, with no cracks, blockages, or algae.
What fixed it
The drain pipe was not cracked. It had no splits, holes, or separated joints anywhere along the run. We removed the loose anchor, drilled a new mounting point into solid wall, and resecured the bracket so the pipe sloped steadily downward to the discharge point. We then poured water through the full run at peak flow to confirm no pooling. No hacking or pipe replacement was needed.
Outcome
The dripping stopped. The pipe now drains freely on both dry and humid days. The wall was left untouched and the original pipe stays in service.
What this case teaches us
Drips tied to humid weather usually mean a drainage problem, not a crack
- A crack drips at the same rate every day. A drip that shows only on humid days means the drain cannot keep up with the extra water.
- Drain pipes can sag over the years as wall brackets work loose. A single low point traps water and backs it up toward the unit.
- Ask for the full drain run to be traced before anyone quotes to hack the wall. A loose bracket is far cheaper to fix.
Related reading
Ready to get started?
Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.