The count
We went back through 25 leak, damp and water-loss investigations in our own job records and separated the bookings that named a suspected cause or location from those that only described a symptom.
| Booking | Investigations |
|---|
| Named a suspected cause or location | 15 |
| Described a symptom only | 10 |
Of the 15 that named something:
| Outcome | Investigations |
|---|
| Confirmed by the investigation | 5 |
| Contradicted by the investigation | 10 |
And of the five that were confirmed, three were right about the room and not the fault. Only two named a component and had that component turn out to be the problem, and one of those two was a tap that was visibly dripping when it was reported.
The ten that were wrong
These are the stated theories, and what the work found:
| What the booking said | What was found |
|---|
| Possible hidden leak on the heating pipework, boiler loses pressure the moment it is topped up | No leak. Tracer gas run twice, nothing. Water discharging from the pressure relief valve, which points at the expansion vessel |
| Water company notice suggesting a slowly leaking toilet or tap | No leak in the property at all. The supply was shared with the flat above, and the discharge was theirs |
| Several plumbers had attended and renewed the silicone, which had not helped | Very small pinholes in both the concealed hot and the concealed cold pipework between a bath and a toilet |
| Customer believes the pipes run through the walls, so tracer gas is needed | A hole in an external four-inch soil pipe at a 45-degree junction. A drainage fault, not a supply one |
| Mould building up in a cylinder cupboard, wanting new leaks ruled out | No leak. Hot, cold and waste all tested sound; every accessible cavity dry |
| Damp present for years, previous engineers unable to find the source | No leak. Hot, cold and heating each held under pressure and under tracer gas |
| Water company notice on the supply pipe, around 100 litres a day | Two WC cisterns passing, one badly, plus a dripping bath tap. Nothing wrong with the supply pipe |
| Tracer gas needed for a suspected concealed leak putting water into a cellar | A blocked gully outside, soaking the masonry. Cleared on the visit |
| Damp marks, leak detection required | No leak. Endoscope found nothing; either a past leak already resolved or ingress through an external wall |
| Constant dripping sound behind a wall, possible leak inside a concealed cistern | No leak. Condensation forming inside the cistern and running down the inside face |
The five that were right
- A leak on the central heating pipework, with the boiler already ruled out by someone else. Correct: a 22mm heating pipe under a floor, gnawed through by rodents.
- A leaking bath tap. Correct, and visible from the doorway. The diverter had failed internally.
- A leak from a shower into the bathroom below. Correct as to the room, wrong as to the mechanism: the bottom row of tiles had lost its grout, and the trap and seal were sound.
- Water from an upstairs bathroom coming through a light fitting below. Correct as to the room: the bath waste pipe had come off its brackets.
- A leak in an upstairs flat going into the commercial unit below. Correct as to the flat: the cold held pressure for 30 minutes and the hot dropped immediately.
Read that list again and the pattern is fairly clean. People are good at identifying which room the water is in, and poor at identifying which component failed. That is not a failure of intelligence; it is a structural problem. You can see the stain. You cannot see the pipe.
Why the theory is usually wrong in the same direction
The contradicted theories fall into three groups, and each has a cause worth understanding.
Water does not appear where it escapes
Water runs along joists, down the back of plasterboard, along the top of a ceiling and out at the nearest low point or the nearest penetration. In one of these jobs, water was gushing through a bathroom ceiling and around the light fitting, and the rooms immediately above had no plumbing in them at all. The source was a pinhole in a pipe inside the ceiling void itself, reached by opening a wall and then the ceiling. In another, the visible moisture was worst at the bath panel, and the pipe that had failed was behind the toilet.
The visible defect is a decoy
In two of the metered-loss jobs, the engineer found a dripping tap within minutes of arriving and recorded, in both cases, that the drip was nowhere near enough to account for the loss. One property was losing around 420 litres an hour. A dripping tap cannot do that, and stopping at the drip would have left the real fault running. If a visible defect does not match the scale of the symptom, it is not the answer.
Damp is not evidence of a leak
Five of the ten wrong theories were damp, mould or a sound interpreted as a plumbing leak. In every one, the plumbing tested sound. Condensation, a resolved historic leak, ingress through an external wall and a defective external drain all produce damp that looks exactly like a supply leak from the inside of the room.
What a competent investigation does instead of guessing
The order used on these jobs is boring and it works. Look first, at everything accessible, and run the fixtures while watching. Then pressure test, which does not find the leak but tells you whether there is one and on which circuit. Only then reach for tracer gas, which needs the circuit drained and gives you an area rather than an exact point. The full sequence is set out here, and the hit rate of each method across these same 25 jobs is worth reading before you ask for a specific technique by name.
That last point matters commercially. Two of these bookings asked for tracer gas by name. One turned out to be an external drain and the other a blocked gully, and neither needed it. Asking for a method rather than describing a symptom narrows what the engineer looks at before they have seen the property.
How to describe the problem so you get the right visit
- Say what you can see and when, not what you think is causing it. "A damp patch on the hall ceiling that grows after anyone showers" is more useful than "a leaking shower waste".
- Say whether it is constant or intermittent, and what it correlates with. Intermittent damp that follows bathroom use points at waste or sealing. Constant loss with everything off points at a pressurised pipe.
- Give the meter reading with every outlet closed, if you have a meter. Two readings an hour apart tell an engineer more than any description.
- Say what has already been tried. The job where several plumbers had renewed the silicone without effect was solved faster because that was in the booking: it ruled the sealing out before anyone arrived.
- Do not remove the evidence. Photographs of the stain at its worst are worth more than a repainted ceiling, especially if there is a claim behind it.
When your theory is probably right, and you do not need us
If you can see water coming out of a specific thing, you are right and you need a plumber, not a detection visit. A dripping tap, a weeping radiator valve, a cistern overflowing into the pan, a visibly wet trap under a sink: all of these were in our records as ordinary repairs, and none of them needed detecting.
The investigation is for the case where you cannot point at the source, or where what you can point at does not explain the damage. Those were the fifteen bookings with a theory, and the theory was wrong in ten of them.
The limits of this count
Twenty-five investigations, fifteen with a stated theory, over nine weeks in one firm's caseload. Fifteen is a very small number and the split could move a long way on another twenty-five jobs. Deciding whether a booking "named a suspected cause" also involves judgement, and we applied it generously: a booking that merely said "leak detection required" was counted as symptom-only even where the caller clearly had a suspicion. The full method, universe and exclusions are set out in the main dataset post.
