Drips Only on Humid Days: Mineral Buildup Narrows the Drain

A landed home drips only on humid days. Whether the pipe has cracked inside the wall or something simpler is narrowing it.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

How this presents

Dripping on and off across a few months, only on genuinely humid days and never on dry ones. The pipe run is old and passes through the wall, so most of it cannot be seen. Cooling itself is unaffected throughout.

Setup: Hitachi Wall-mounted7-9 yearsLandedBishan
Misread as: A cracked pipe inside the wall, and the hacking needed to reach it.
Check first: Whether the drip tracks humidity, then the whole run traced joint by joint

What else produces this

Weather correlation separates a break from a restriction before anything is opened. A crack leaks steadily regardless of output, because water is escaping rather than backing up. A narrowing passes ordinary volume perfectly and fails at peak, which is exactly what a humid day produces. That points along the run rather than at the unit, and a run can be traced joint by joint without touching the wall.

A pipe run near the unit with even slope and no dip or sag removes the obvious routing fault.
A hard chalky buildup narrowing the bore at one joint further along is a restriction, not a break.
Backing up toward the unit on high-output days, and clearing on ordinary ones, is a margin that has run out.
Free flow through the whole run at peak volume after clearing confirms nothing else along it is narrowed.

Why it happens

Condensate carries dissolved minerals, and where it slows at a joint they come out of solution and stay. The deposit builds inward, a layer at a time, across years. The bore narrows without the pipe developing any fault at all: no crack, no sag, no loose bracket. Ordinary output still passes through. Peak output does not, and the surplus has nowhere to go but back toward the pan.

What resolution involves

Clear the deposit from the affected joint and confirm the bore is back to its original width. Then pour water through the whole run at peak volume, because one narrowed joint means the conditions for narrowing exist everywhere along it, and the next one is worth finding now rather than next season. No hacking, no re-levelling and no pipe replacement follows from this.

How to tell it worked

Test at the volume that caused it, through the entire run rather than past the joint that was cleared. A margin is only proved at the flow that exhausted it.

Before you approve a quote

A leak that follows the weather is a capacity problem

A crack leaks at the same rate every day. A restriction only fails when volume peaks.
Ask for the full run to be traced before anyone quotes to open a wall. The fault is often past the visible part.
Minerals narrow a pipe from the inside without anything ever falling into it.

Questions this case answers

Aircon drips only on humid days and stays dry otherwise: why?

Because the drain copes with ordinary output and runs out of margin at peak. Humid weather makes far more condensate, and a path that is narrowed somewhere along it passes the smaller flow perfectly while the larger one backs up. A crack would leak the same amount on a dry day.

Can a drain pipe get blocked without anything falling into it?

Yes, and it is common on older runs. Condensate carries dissolved minerals, and where the water slows at a joint they deposit on the inside wall a layer at a time. The bore narrows from within, with nothing entering the pipe from outside at all.

Will the wall need hacking to fix a drain problem in an older house?

Not before the accessible run has been traced. The visible sections and the joints at either end are usually enough to find a restriction, and the fault is frequently past the part everyone assumes is fine. Opening a wall is the last step, not the first.

What should be checked before anyone quotes to open a wall?

The whole accessible run, joint by joint, and a flow test at peak volume. If water passes freely at the rate a humid day produces, the buried section is not the problem, and that result is worth having before anyone prices demolition.

Describe your situation

Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.

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