A leak under the bath is usually found by timing when it happens: while filling, while draining, or only when the shower runs over the bath. That timing points to the panel, waste, overflow, or a supply pipe as the source. Access panels or a small opening usually reach it. Locating the exact point first, rather than lifting tiles on a guess, is the difference between a small repair and a big one.
In This Guide
Why bath leaks are hard to pin down
A bath sits over a boxed-in void that hides most of its plumbing: the waste trap, the overflow pipe, the taps' supply connections, and often a run of pipework passing through on its way to somewhere else entirely. When water appears on the ceiling below or a damp patch spreads across the bathroom floor, several different things could be responsible, and they’re all out of sight at once.
This is different to a leak under a sink, where the pipework is usually visible the moment you open the cupboard door. Under a bath, everything is boxed in behind panelling, and in many older Scottish bathrooms that panel is tiled over or sealed with silicone, making it feel like the only way in is to break something.
It doesn’t have to be that way. A leak under bath problems can almost always be narrowed down before anything gets opened up, just by paying attention to when the water appears.
Diagnosing by timing
The single most useful piece of information is when the leak shows itself. Water appearing at different points in a bath’s use cycle points to different sources, and this costs nothing to check.
- Leak appears while the bath is filling. Suggests the supply pipes or tap connections under the bath, since these are only under pressure while water is running in.
- Leak appears while the bath is draining. Points to the waste trap or the pipe running from the plug to the main waste stack.
- Leak appears only when the bath is very full. Suggests the overflow pipe, which only carries water once the level gets close to the rim.
- Leak appears whenever the shower over the bath runs. Points to the shower mixer, hose connection, or a gap in the sealant around the bath edge rather than the bath’s own plumbing.
- Leak appears constantly, bath in use or not. Suggests a supply pipe leak unrelated to bath use, which is worth investigating as a standalone plumbing issue.
Testing the waste and overflow separately
Filling the bath a little, then pulling the plug and watching underneath (or checking the ceiling below, if that’s the only access) isolates the waste and overflow from the supply side entirely. Running the taps briefly with the plug in tests the supply connections on their own. Two short tests tell you far more than a general damp patch does.
Fill, drain or overflow: what each pattern means
Once you know roughly which stage triggers the leak, the likely culprits narrow considerably.
| Timing | Likely source | Typical access needed |
|---|---|---|
| While filling | Tap tails, supply pipe joints | Access panel at tap end |
| While draining | Waste trap, waste pipe joints | Access panel at waste end |
| Bath nearly full | Overflow pipe | Access panel, sometimes behind bath |
| Shower running | Mixer, hose, sealant gap | Often no access needed, check sealant first |
Not every leak fits neatly into one row. A worn seal around the waste, for instance, can leak during both filling and draining if water pools around the plughole area throughout the bath’s use. That’s where timing alone isn’t quite enough and a proper look underneath, or a specialist survey, settles it.
Access panel options
Most modern baths are panelled rather than tiled directly onto brick, which makes access far easier than people expect.
Clip-in or screwed panels
Many bath panels simply clip into place or are held with a handful of screws. These come away cleanly and go back on without damage, giving full access to the void underneath.
Cut-in access hatches
Where a panel is tiled over and can’t be removed whole, a small hatch can be cut into the panel itself, away from any tiled section, and fitted with a discreet cover for future access.
Access from an adjoining space
In some layouts, the bath’s plumbing is reachable from a cupboard, loft hatch, or the room on the other side of the wall, avoiding the bathroom’s finished surfaces altogether.
The point of finding the leak’s exact location first is that it tells you which of these options actually gets you there. There’s no sense cutting a hatch on the taps' end of the bath if the leak is at the waste end, three feet away behind a different section of tile.
Why detection-first beats exploratory tiling
The instinct when water is coming from somewhere under a bath is to start removing things until the source turns up. That approach can work, but it’s expensive when it doesn’t, and bathroom tiling is one of the costliest finishes to replace by guesswork.
We use thermal imaging and acoustic listening to read what’s happening under the bath and behind the surrounding tiles before anything gets opened up. Thermal imaging picks up temperature differences where water is sitting or moving. Acoustic equipment picks up the sound of water escaping under pressure, even through tile and board. Combined, they usually narrow a bath leak to a specific small area, sometimes to within a single tile.
That precision matters because it changes the repair from "open up half the bathroom" to "open up this one section". For anyone weighing up whether to call a plumber or a specialist first, our guide on choosing between a leak detection specialist and a plumber covers exactly this kind of decision.
If the ceiling below the bathroom is bulging, sagging, or has a large wet patch, stop using the bathroom above it and get it checked immediately. A saturated ceiling can collapse without warning, so treat this as a safety issue that needs attention now, not a repair to schedule for later.
Find the leak before you touch a tile
We use non-invasive thermal imaging and acoustic listening to pinpoint bath leaks precisely, so you know exactly which panel or section needs opening before any work starts.
Insurance and trace and access cover
Most buildings insurance policies include trace and access cover as standard, which pays for the cost of finding a leak and accessing it, including lifting tiles or cutting into a panel, along with making good the damage caused by that search. Price-comparison service Confused.com notes most policies cover up to about £5,000 of trace and access costs, though it is worth checking your own schedule rather than assuming.
Trace and access cover pays for finding and reaching the leak. It does not pay for repairing the pipe, tap or waste itself once found. That distinction matters when you’re weighing up whether to claim: the search is usually covered, the fix usually isn’t. Our trace and access service produces exactly the report an insurer needs to process that side of a claim.
Honestly, most bath leaks we’re called to turn out to be the waste seal or a loose tap connector, nothing dramatic. But getting a proper report in place before repair work starts means the insurance side is straightforward if you do need to claim.
When to call a specialist
If you can see the leak clearly once the panel is off, and it’s a simple job like a loose olive on a compression joint, a plumber can usually sort that on the spot. Call a leak detection specialist when the source isn’t obvious once the panel is removed, when water is tracking to a spot some distance from the bath itself, or when the leak keeps recurring after a repair.
Our non-invasive methods, combined with insurance-approved reporting, mean you get a clear answer without unnecessary demolition. That approach sits behind a 99% success rate across more than 5,000 leaks found, most of them without a single tile broken.
Frequently Asked Questions
Look for damp patches on the ceiling below the bathroom, staining on skirting boards near the bath, or a musty smell that doesn’t clear with ventilation. Note whether the damp appears while the bath fills, drains, or only when it’s very full, since that points to the source.
Usually not. Most baths have a removable or clip-in panel that gives full access without touching tiles. Where tiles are fixed over the panel, a specialist survey first narrows down exactly where the leak is, so only the necessary section needs opening.
This points to the overflow pipe, which only carries water once the bath level gets close to the rim. It runs from the overflow slot to the waste pipe, and a failed joint or seal there only shows up under that specific condition.
Most buildings insurance includes trace and access cover, which pays for finding and reaching the leak and making good the damage from that search, commonly up to around £5,000. It does not cover the cost of repairing the leaking pipe, tap or waste itself.
A slow leak under the bath can track along a joist or pipe run before showing as a stain some distance from the actual source. This is why exploratory work often misses the mark: the visible sign and the real leak point aren’t always in the same spot.
Yes. If the leak only appears when the shower over the bath runs, the cause is often the shower mixer, hose connection, or a gap in the sealant along the bath edge, rather than anything in the bath’s own supply or waste plumbing.
That depends entirely on where the leak actually is, which is why locating it precisely first matters. A pinpointed leak often needs only a small hatch or a single panel removed, compared with lifting a large area of tiling on a guess.
📍 Professional Leak Detection Across Scotland
Don’t let a small problem become a big one
We find bath leaks precisely using non-invasive methods, so repairs stay small and your insurer gets the report they need.