Choosing between companies you cannot assess technically is the hard part of a hidden leak. Six questions separate a survey from a guess, and the answers tell you more about the outcome than any review ever will.
Choosing a leak detection company is uncomfortable because you are buying something you cannot evaluate. You cannot tell from a website whether a company will find your leak, and by the time you can tell, you have already paid. Reviews do not help much either, because a happy review usually means somebody turned up and was pleasant, which is not the same as the leak being found on the first visit.
What does help is knowing which questions separate a structured investigation from an expensive guess. There are about six of them, they take five minutes on the phone, and the answers are more predictive of the outcome than anything else available to you. This guide sets them out, along with what a competent survey should actually include, what the written report has to contain to be worth anything, and the warning signs that reliably precede a second visit.
What You Are Actually Choosing Between
Three different trades will answer an advert for a leak, and they do different jobs. Getting this wrong is the commonest reason a first visit achieves nothing.
| Who | What they are good at | Where they struggle |
|---|---|---|
| General plumber | Repairing a failure you can point at, replacing valves and fittings, isolating a system | Locating anything concealed, because the toolkit is for repair rather than diagnosis |
| Drainage contractor | Blockages, CCTV survey of waste and soil runs, drain condition | Pressurised supply and heating leaks, which do not appear on a drain camera |
| Leak detection specialist | Finding a concealed source by eliminating systems and narrowing the area before anything is opened | Nothing, if the problem is visible, in which case you are overpaying for diagnosis you do not need |
The difference that actually matters
A plumber fixes what is in front of him. That is exactly right for a burst on an exposed pipe and exactly wrong for a stain with no visible origin, because the only way a repair trade can find a concealed leak is by opening up until it appears. Every hole is a guess, and the guesses are charged for whether or not they were right. A detection specialist works the other way round: eliminate the systems that are sound, narrow the area, then open one defined aperture. Our comparison of a leak detection specialist and a plumber sets out where the line falls.
When a plumber is the right call
Call a plumber, not a detection company, when you can see the water coming from a specific place: a dripping compression joint under a sink, a weeping radiator valve, an overflowing cistern, a failed flexible hose on an appliance. Paying for detection when the source is visible is paying for a diagnosis that has already been made. The specialist is for the cases where nobody can point at anything.
The Six Questions to Ask Before Booking
Ask these on the phone, before a date is agreed. Each one has a right answer and a revealing wrong one.
| Question | What a good answer sounds like | What a poor answer sounds like |
|---|---|---|
| What methods will you bring? | Several named, with a reason tied to my floor construction and which systems are live | One instrument named as though it works everywhere |
| Is a written report included? | Yes, with readings, method, photographs and a named failed component | We can do you a report, or the engineer will tell you on the day |
| What does the fee cover and for how long? | A defined scope, with a stated position on what happens if it runs over | A fixed price with no scope, or a rate with no ceiling |
| Is opening up included? | No, and here is how it is scoped and quoted once the area is narrowed | Vague, or a figure that quietly assumes a floor will come up |
| Do you carry out the repair as well? | Either answer is fine, provided it is disclosed | Evasive, which usually means the survey is a route to a repair quote |
| What happens if you do not find it? | A clear statement of what is charged and what the report will still establish | We always find it |
The last one is the most diagnostic. Nobody always finds it. A company that says so is either inexperienced or managing you, and both tend to end with an invoice for a visit that eliminated nothing on the record.
What a Competent Survey Actually Includes
A survey is a sequence, not a gadget. The order matters because each step removes possibilities, and a company that starts with the camera rather than the meter is working backwards.
| Step | What it establishes | Typical equipment |
|---|---|---|
| Isolation test at the meter | Whether the incoming supply is losing water with every outlet closed | Water meter, internal stop tap |
| Pressure testing by section | Which system has a breach, and which are sound | Gauge and test pump on an isolated run |
| Moisture mapping | The extent of wetting and the direction water travelled | Capacitance meter, pin or resistance meter |
| Thermal survey | Hot water and heating leaks, pipe routes under screed | Infrared camera |
| Acoustic survey | Position along a pressurised supply run | Ground microphone, listening stick, correlator |
| Tracer gas | Small breaches under screed, slab or underfloor heating | Hydrogen or nitrogen mix and a sniffer probe |
| Controlled access | Visual confirmation of the named component | Board lifter, core cutter, defined aperture |
Why one instrument is not a survey
Every method has a blind spot, and a company carrying one method has that blind spot permanently. Thermal imaging reads surface temperature rather than water, so it performs well on hot water and heating and poorly on cold supply, and it is largely defeated by thick floor insulation or a finish with high thermal mass. Acoustic equipment listens for water escaping a pressurised pipe, so it does close to nothing on a gravity waste run, on a system that has been drained, or on plastic pipe under deep screed where the sound is absorbed before it reaches a microphone. Tracer gas needs a section that can be isolated and drained, which rules it out where valves are seized. Moisture mapping shows where water arrived, not where it started, and on an insulated floor those two points can be metres apart. If one method were sufficient, the trade would only own one. Our guide to what a leak detection survey involves takes the sequence step by step.
Ruling a system out is a result
A survey that proves the heating circuit holds pressure for a stated duration, the supply is static at the meter and the waste stack is sound has narrowed the problem substantially, even without putting a finger on the failure. That is a finding, and it should be written down. It only looks like a failure when nobody records what was tested, at what pressure and for how long, which is why the report matters as much as the fieldwork.
What the Written Report Should Contain
The report is the deliverable. Fieldwork that nobody can reconstruct three months later has not been bought, it has been rented for an afternoon. Ask to see a redacted example before booking. Any company that produces them regularly will have one.
| Element | What it must state | Why it matters later |
|---|---|---|
| Instruction and dates | Who instructed, date of discovery, date attended, date of report | The sequence of dates is what any later dispute turns on |
| Property and systems | Construction, floor build-up, pipe material and route | Explains why a given method was chosen or was unavailable |
| Method in sequence | Each technique used, why, and what it ruled in or out | Shows the search was proportionate before anything was opened |
| Readings | Moisture values with the instrument named, pressure test results with durations | Makes the finding reproducible rather than asserted |
| Photographs | Referenced to a room or plan, before and after any opening up | Lets a reader who was never on site see what was found |
| Findings | The failed component named, the failure mode described | A room is not a cause; a component is |
| Scope of works | What repair is needed, what reinstatement is needed, what is out of scope | Stops the next trade repricing from scratch |
Naming the component, not the room
Bathroom leak is not a cause. A failed compression joint on a concealed hot feed is a cause. A perished seal where a shower tray meets a tiled upstand is also a cause, and the two are dealt with in completely different ways despite producing an identical stain on the ceiling below. A report that says water ingress in bathroom has told you nothing you did not know before you picked up the phone. Where a third party has commissioned the work rather than the householder, the report has to do more still, and those requirements are set out in our specification for leak detection for loss adjusters and insurers.
Credentials, and What Is Worth Verifying Yourself
There is no single statutory licence for leak detection in the United Kingdom, which is why the word specialist on a website carries no weight on its own. What does exist is verifiable, and it takes a few minutes:
- Public liability insurance, with a current certificate you can read rather than a logo. Ask for the certificate, not the claim.
- Registration on a recognised plumbing scheme where any repair or test connection will touch the wholesome water supply. WaterSafe holds a searchable national register of approved contractors, and Thames Water directs customers to it.
- Compliance with the Water Supply (Water Fittings) Regulations 1999, which prohibit materials likely to contaminate the supply. This applies to a temporary test connection as much as to a permanent repair.
- A company number and a registered address that match the trading name on the quote.
- A written quotation with a scope, not a text message with a figure.
Reviews, and what they do not tell you
Reviews measure conduct, not competence. Punctuality, tidiness and politeness are visible to a customer and therefore get reviewed. Whether the survey sequence was sound, whether a system was properly eliminated and whether the report would stand up is invisible to the person writing the review. Read them for red flags, particularly any pattern of return visits or of a quote changing on site, and ignore them as evidence of technical quality.
The Warning Signs
Any one of these is worth a second call to somebody else.
- A firm price quoted before anyone has asked what the floor is made of or which systems are live.
- A single method described as though it works on every property.
- Pressure to authorise opening up on the first visit, before anything has been narrowed down.
- No written report included, or a report that turns out to be a photograph and a sentence.
- An unusually low headline figure on a complex property. Our note on the real cost of cheap leak detection covers where the difference reappears.
- A guarantee that the leak will be found, with no statement of what happens if it is not.
- A survey fee that is waived if you accept the repair quote, which makes the diagnosis a sales call.
- No fixed address, no company number, and a mobile number only.
The quote that assumes the answer
Watch for a quote that already prices a repair. If a company can tell you what the repair will cost before it has located anything, it has decided what it expects to find, and confirmation bias on site does the rest. The honest sequence is survey, then a scoped repair quote based on what was actually found.
Comparing Two Quotes Fairly
Quotes for the same property routinely differ by a factor of three, and the difference is usually scope rather than greed. Before comparing figures, make the two quotes describe the same job:
- Does each include a written report, or only one of them?
- Is each an attendance for a fixed window or open-ended time, and what happens at the end of the window?
- Does either include controlled opening-up, or is that quoted afterwards?
- How many systems has each assumed has to be eliminated?
- Is either priced on the assumption that it will also carry out the repair?
- Are detection, access and repair on separate lines, or rolled into one figure?
Our note on why leak detection quotes differ so much in London works through the same comparison in detail. Once both quotes describe the same scope, the decision is usually obvious, and it is frequently not the cheaper one.
How we help with this
If the article describes a problem you actually have, these are the visits that deal with it.
- our full guide to leak detection
How each method works and when it is the wrong tool for the job.
- leak detection in London
Finding a hidden leak without opening the property up first.
Frequently asked questions
Should I call a plumber or a leak detection company?
It depends on whether you can point at the water. If the source is visible, such as a dripping joint under a sink or a weeping radiator valve, a plumber is the right call and detection adds nothing. If there is a stain, a damp patch, unexplained meter movement or heating pressure loss with no visible origin, a repair trade can only find it by opening up until it appears, and every hole is a guess you pay for. That is the case for a specialist.
What is the single most useful question to ask on the phone?
Ask what happens if they do not find it. A company that answers with a clear statement of what is charged and what the report will still establish has thought about the case where elimination is the outcome, which is common. A company that says it always finds them is either inexperienced or managing you. The follow-up worth asking is which methods they will bring and why, because a reason tied to your floor construction shows they have understood the property.
Do I need the written report if I just want the leak fixed?
If the source is visible and the repair is immediate, probably not. For anything concealed, the report is most of what you are buying. It records which systems were tested, at what pressure and for how long, what the moisture readings were and which instrument produced them, and names the component that failed. Without it you have paid for an opinion that cannot be checked, cannot be handed to the next trade, and cannot be used if the finding is ever questioned.
Are accreditations worth checking, or are they just logos?
Some are verifiable and some are decorative. There is no single statutory licence for leak detection in the United Kingdom, so the word specialist means nothing by itself. What can be checked is a current public liability certificate rather than a badge, registration on a recognised plumbing scheme where work will touch the drinking water supply, and a company number matching the trading name on the quote. WaterSafe maintains a searchable national register, and Thames Water directs its own customers to it.
Why is one quote three times the other for the same job?
Almost always scope rather than greed. Typically one includes a written report and the other does not, or one is a fixed window with no stated position on overrun, or one has priced controlled opening-up and the other will quote it afterwards, or one has assumed a single suspect system while the other has counted five. Make both quotes describe the same job before you compare the figures. The cheaper one frequently turns out to be a shorter, narrower piece of work.
Is it a problem if the same company finds and fixes the leak?
Not in itself, and it is often convenient, but it should be disclosed before you book. The arrangement to be careful of is a survey fee waived if you accept the repair quote, because that turns the diagnosis into a sales call and rewards finding something expensive. The safer structure is a survey priced on its own terms, a written finding, then a repair quote scoped from what was actually located. You are then free to take that scope elsewhere.