How does acoustic leak detection work through a wall?
Water escaping a pressurised pipe makes noise, even a pinhole. Acoustic detection uses a ground and wall microphone with amplification tuned to the frequencies leaks produce. We work along the suspected pipe run, comparing the sound signature at each point, and the leak is loudest directly over the breach. On brick and block walls the sound carries well. On plasterboard over timber framing it can echo, so we combine acoustics with the other methods below rather than trusting one reading. This is the same approach covered in more detail on our acoustic leak detection page, applied vertically instead of under the ground.
When is thermal imaging the right tool?
A thermal camera does not see water. It sees temperature difference. A hot water line leaking inside a wall paints a warm plume across the plaster that the camera picks up instantly, and an evaporating cold water leak often shows as a cool patch. Thermal imaging is quick and completely non-invasive, so we usually sweep the wall with the camera first to shortlist suspect zones, then confirm with acoustics or moisture readings. Its honest limitation: a small cold water leak deep in a cavity brick wall may not create enough surface temperature change to show, which is why we never quote a repair off a thermal image alone.
How does pressure testing narrow it down?
Pressure testing tells us which line is leaking before we hunt for where. We isolate the hot and cold systems separately, pressurise each, and watch the gauge. A hot side that drops while the cold holds steady immediately halves the search area and often points straight at the hot water system's pipe runs. On homes with multiple wet areas we can isolate branch by branch. It is methodical rather than clever, and it is the step that stops walls being opened on a guess.
Which method finds which leak?
| Method | Best at finding | Wall damage to test | Typical role in the job |
|---|---|---|---|
| Thermal imaging | Hot water leaks, wet plumes behind sheeting | None | First-pass sweep |
| Acoustic listening | Pressurised pipe leaks, any temperature | None | Pinpointing the breach |
| Pressure testing | Confirming which line and system is leaking | None | Isolating hot vs cold, branch by branch |
| Moisture meter mapping | Spread of dampness, shower and waterproofing failures | None | Separating pipe leaks from shower leaks |
What are the most common causes of leaks behind walls?
Knowing what usually fails changes where we point the gear first. The braided flexi hoses feeding taps and toilets are the biggest single culprit in modern homes, and they hide in vanity cabinets and behind washing machines rather than deep in the wall, which is good news for your plasterboard. The hose itself costs $20 to $40 at trade rates, and replacing them proactively every 5 to 10 years is the cheapest insurance in plumbing. After flexis come failed shower waterproofing and grout, weeping tap bodies and mixer cartridges inside the wall, and corroded fittings at pipe joints. Genuine mid-wall pipe breaches are actually the least common of the lot, especially in homes plumbed in copper or PEX, which is why we test before we cut rather than assuming the worst and most expensive cause.
Will the wall ever need to be cut anyway?
Sometimes, and we would rather tell you that up front. Detection locates the leak; repairing it still means accessing the pipe, which usually needs a neat access hole at the located point. The difference is one controlled cut of a few hundred millimetres instead of exploratory demolition across a whole wall. The other honest scenario: when testing shows the pipes are sound and the real problem is failed shower waterproofing, the fix is a tiling and sealing conversation, not a plumbing patch, and we will say so rather than sell you a repair the wall does not need.
What does it cost, and what do I get?
As of 2026 our leak detection is $200 to $500 or more depending on access and how elusive the leak is, quoted as a fixed price before we start, never by the hour. You get the leak located and marked, an explanation of the cause, and a fixed quote for the repair. If the repair is a straightforward accessible burst, that work typically runs $250 to $650 plus parts.
Water stain spreading on a wall? Call Hills Plumbing & Gas on 0472 657 042 or book at /services/leak-detection/. QBCC licence 15243081, and we find it before we cut it.