How do I know if my shower tray is cracked or just the seal has gone?

Block the waste, fill the tray with water and leave it twenty minutes with nothing else running. A drop in level or water below means the tray or its bed. If the tray holds water perfectly but leaks when the shower runs normally, the water is getting in above the tray, at the seal, the grout or the screen.

Why does my shower leak only sometimes?

Because something about the conditions changes. The usual patterns are leaks that need weight in the tray, leaks that need a sustained run to saturate the grout, and leaks that only happen when the screen gets sprayed directly. Note what was different on the occasions it leaked and the cause is usually obvious.

Can a shower leak damage a ceiling without any water showing in the bathroom?

Routinely. Water passing through a failed seal or a cracked tray goes straight into the floor void, so the bathroom floor stays dry while the plasterboard below absorbs it. The first sign is usually a stain or mould on the ceiling underneath.

Do I have to rip out the bathroom to find a shower leak?

No. The four isolation tests, moisture mapping, thermal imaging and tracer gas identify the fault before anything is opened, and access is usually taken from the ceiling below rather than from the bathroom side.

Is a wet room more likely to leak than a tray?

It has fewer components but a larger single point of failure. A wet room depends on a continuous tanking membrane under the tiles, and if that was applied badly or damaged during the tiling, the leak is diffuse and cannot be sealed from the surface. It needs stripping back to the membrane.

A Leaking Shower: Tray, Seal, Waste or Pipe

Run the shower for ten minutes with the door shut and nobody standing in it. If it still leaks, the fault is the tray, the waste or the pipework. If it only leaks when someone is in it or the screen gets sprayed, it is the seal, the grout or the glass.

Leak Fix LondonLast updated 19 September 2026

A Leak Fix London engineer working on pipework in a London home

Four tests, in this order

A shower has four independent ways of leaking and they are almost impossible to tell apart by looking. They are easy to tell apart by controlling which one you expose at a time. Do these in order and stop at the first one that reproduces the leak.

Waste only. Block the shower with nothing running, then pour two or three litres of water directly down the waste from a jug, slowly. Nothing else gets wet. If water appears below, the fault is the waste connection or the trap.
Static tray. Block the waste with a proper test plug or a well-packed cloth, fill the tray with 20 to 30mm of water, and leave it for twenty minutes without touching anything. If the level drops or water appears below, the tray itself or its seal to the floor has failed.
Spray only. Empty the tray. With the head detached or aimed deliberately, wet only the screen, the door seal and the junction between the screen and the tray, avoiding the walls above. A leak here is the door seal, the screen fixing or the silicone under the screen profile.
Full running use. Run the shower normally for ten minutes with the door shut and nobody inside, then repeat with someone standing in it. A leak that only appears with weight in the tray is movement, not sealant.

Write down which test produced water and how long it took. That single observation removes most of the guesswork, and it is the thing an engineer will ask you first.

What each fault looks like

Fault	When it leaks	Where the damage shows	What it needs
Silicone at the tray-to-wall junction	Only when that joint is sprayed or splashed	Immediately below that wall, close to the tray	Strip and reseal properly
Grout and tile bedding failure	After sustained use, and worsening over months	On the wall below, sometimes a metre from the shower	Rake out and re-tile the affected area
Waste or trap connection	Only while water is running away	Directly beneath the waste	Replace the seal, or refit the trap squarely
Tray cracked or poorly bedded	When weight is in the tray	Under the tray, worse the longer the shower runs	Re-bed the tray, or replace it
Concealed valve or supply pipe	Constantly, including with the shower off	Anywhere along the pipe run, often not near the shower	Locate and repair the pipe
Wet-room tanking failure	Sustained use, spreading slowly	A large, diffuse area below	Strip back, re-tank and re-tile

The row that catches people out is the fifth. If the ceiling below is wet when the shower has not been used for two days, stop testing the shower. That is a supply pipe, and it has nothing to do with the tray. Turn the water off at the stopcock and get it looked at.

The fault nobody checks: movement

A shower tray sitting on a floor with any spring in it will crack its seal no matter how carefully the silicone was applied, because the joint opens and closes every time someone steps in. On a timber floor, a tray bedded on a few dabs of adhesive rather than a full bed will flex at the unsupported points. Standing in the tray and shifting your weight, listening for a creak or watching the silicone line at the wall, finds this in thirty seconds.

The standards treat wet areas as a different problem from ordinary internal tiling for exactly this reason. BS 5385-4:2015 gives recommendations for the design and installation of ceramic and mosaic tiling in specific conditions, including wet areas and conditions that are potentially detrimental to the installation, and is separate from BS 5385-1, which covers normal internal conditions. A shower built to the normal-conditions rules, on a substrate that moves, will leak eventually regardless of how much sealant goes into it.

How to reseal so it lasts

Most resealing fails within a year, and it usually fails for the same three reasons.

Remove all of the old silicone. New sealant will not bond to old sealant. Cut it out with a blade, then clean the residue off with a silicone remover, not just a scraper.
Let it dry. If the joint has been leaking, the substrate behind it is wet. Give it at least 24 hours with the shower unused and the room ventilated. Sealing a wet joint traps the water behind it.
Load the tray first. Fill the tray with water, or stand in it, before you apply the sealant, and leave it loaded until the sealant skins. The joint is at its widest under load, so a bead applied to an empty tray gets stretched and torn the first time someone uses the shower.

Use a sanitary-grade silicone with a mould inhibitor, tool it once in a single pass, and do not use the shower for the full cure time on the tube rather than the two hours you can get away with.

What to do while you work it out

If water is reaching a ceiling below, stop using that shower entirely rather than using it carefully. A shower used once a day keeps the void wet continuously, and the damage from four more weeks of that is usually larger than the cost of the repair.

If there is a bath in the same room, use it, but check first that the bath is not the actual source. The overlap between a leaking shower over a bath and a leaking bath seal is the single most common misdiagnosis in this trade, and the test is the same: fill the bath, leave it, then drain it and watch for the difference between a static leak and a leak on discharge.

Turn the extractor on and leave the bathroom door open so the floor and the void below get some air movement. That does not dry a saturated void, but it slows what is happening in the plaster underneath.

When resealing will not work

The leak happens with the shower off.
Water appears well away from the shower, on the far side of a room or a metre along a ceiling.
The ceiling below is stained but the bathroom floor is dry.
The same joint has been resealed more than twice.
The tray moves, creaks or rocks.
It is a wet room rather than a tray, in which case the tanking membrane is the thing that has failed and sealant is irrelevant.

And if what you actually have is a head that keeps dripping into the tray with the shower off, that is the valve, not the enclosure: see shower head dripping.

Finding it without taking the bathroom out

The default in this trade is to strip the shower, which is why people leave a leaking shower running for a year. It is not necessary. The four tests above are done with the moisture readings watched rather than by eye, so a change of a few percent in the substrate below shows up long before water becomes visible. Thermal imaging picks up the hot supply run behind the tiles and shows where it is losing heat into the wall. Where the leak is on pipework rather than the enclosure, the pipework is isolated and drained and tracer gas is introduced, which will find a pinhole behind tiles without a single tile coming off.

Access, when it is needed, is taken from the ceiling below wherever the construction allows, because a 300mm opening in a ceiling is a much smaller job to put right than a stripped bathroom. And putting it right is part of the job here: bathroom and shower leak repair includes the retiling, the replastering and the decoration, not just the plumbing.

What it costs

Detection is £150 per hour, fixed before we attend, and if we do not find the leak you do not pay for the time spent looking. A shower is usually one of the quicker jobs, because the four tests isolate it quickly. Repair and making good are quoted once the fault is identified. See pricing, and if the water is already coming through the ceiling below, start with a shower leaking through a ceiling.

Frequently asked

How do I know if my shower tray is cracked or just the seal has gone?: Block the waste, fill the tray with water and leave it twenty minutes with nothing else running. A drop in level or water below means the tray or its bed. If the tray holds water perfectly but leaks when the shower runs normally, the water is getting in above the tray, at the seal, the grout or the screen.
Why does my shower leak only sometimes?: Because something about the conditions changes. The usual patterns are leaks that need weight in the tray, leaks that need a sustained run to saturate the grout, and leaks that only happen when the screen gets sprayed directly. Note what was different on the occasions it leaked and the cause is usually obvious.
Can a shower leak damage a ceiling without any water showing in the bathroom?: Routinely. Water passing through a failed seal or a cracked tray goes straight into the floor void, so the bathroom floor stays dry while the plasterboard below absorbs it. The first sign is usually a stain or mould on the ceiling underneath.
Do I have to rip out the bathroom to find a shower leak?: No. The four isolation tests, moisture mapping, thermal imaging and tracer gas identify the fault before anything is opened, and access is usually taken from the ceiling below rather than from the bathroom side.
Is a wet room more likely to leak than a tray?: It has fewer components but a larger single point of failure. A wet room depends on a continuous tanking membrane under the tiles, and if that was applied badly or damaged during the tiling, the leak is diffuse and cannot be sealed from the surface. It needs stripping back to the membrane.

Sources

No find, no fee · £150 per hour. The rate is fixed before we attend and does not rise for a difficult property, an awkward access or an evening visit. The total depends on how long the job takes; the rate cannot change.