A leak you can’t see is doing damage you can’t yet measure. Every leak detection engineer listed here is verified, insured and locally based — covering all London boroughs and the City.
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Every listing is verified before it goes live — insurance checked, service coverage confirmed and contact details validated. No paid placements go live without verification — listing comes after checks, not before.
Already know your borough? Jump to the borough grid below. Contact 2–3 verified engineers to compare methods and pricing, and confirm they use non-invasive detection equipment before anyone attends.
If an engineer proposes opening floors or walls before attempting non-invasive detection, get a second opinion — modern leak detection should not begin with invasive opening work.
Compare Verified Leak Detection Engineers in Your Borough — Call Now →
Signs you have a leak — and what to do before calling an engineer
Rising water bills with no change in usage
An unexplained increase in water bills is one of the earliest indicators of a concealed leak. Thames Water offers a bill credit for water wasted during a confirmed supply pipe leak — the cost of repair remains yours.
To qualify, the repair must be completed within four weeks of identification and the claim submitted within three months of the repair date. Note your meter reading before and after a 30-minute period of zero water use. If the meter moves, there is a leak on the supply side.
Damp patches, staining or mould — no obvious cause
Damp patches on walls, ceilings or floors without an obvious source are a common indicator of a concealed pipe leak or a failed joint behind the surface.
In London’s Victorian terrace stock, original pipework runs through wall cavities and under suspended timber floors — leaks in these locations can run for months before surface evidence appears.
Note the location, photograph it and track whether it grows or changes before calling.
Drop in boiler pressure — no visible leak
A sealed central heating system that repeatedly loses pressure without a visible leak has a concealed leak somewhere in the system — most likely in pipework buried under a floor or behind a wall.
Do not keep topping up the pressure without investigating. A pressure drop of more than 0.5 bar per week with no visible cause warrants a leak detection visit.
Sound of running water — nothing turned on
Audible water movement when all fixtures are off is a strong indicator of an active supply pipe leak.
The sound is often most audible at night when ambient noise levels drop. Note where in the property the sound is loudest — this narrows the search area for the engineer.
Subsidence or ground movement near external pipework
Soft patches in gardens, sinkholes near pathways, or unexplained ground subsidence near the property boundary can indicate a leaking buried supply pipe.
London clay soil responds dramatically to water saturation — a leaking pipe under a garden will cause localised ground movement that worsens over time.
Leak detection methods — what a London engineer should use
Acoustic leak detection
Ground microphones and acoustic correlators identify the sound signature of water escaping under pressure — the frequency and intensity of the sound changes at the leak point.
Acoustic detection is effective on supply pipes under solid floors, driveways and gardens. It is non-invasive and produces a precise location before any opening up is required. This is the standard first-line method for supply pipe leaks in London properties.
Thermal imaging
Infrared cameras detect temperature differentials in walls, floors and ceilings caused by water movement.
Warm water leaks from heating pipework and cold supply leaks both produce thermal signatures that are visible without any opening up.
Thermal imaging is particularly effective in London’s Victorian terrace stock where pipes run through original wall cavities. It is not effective through thick stone walls or deep subfloor voids.
Tracer gas detection
A non-toxic mixture of nitrogen and hydrogen — typically 95% nitrogen, 5% hydrogen — is introduced into the pipe under pressure.
Hydrogen is the smallest molecule available and can penetrate solid concrete, timber flooring and most floor tile types, making it particularly effective under underfloor heating screeds without requiring the system to be drained first.
The gas escapes at the leak point and is detected at the surface by a sensitive probe. Tracer gas detection is the most precise method available and is used where acoustic detection cannot isolate the exact leak location, or where pipes run under deep concrete floors or external hardstanding.
Endoscope and borescope inspection
A small camera is inserted through a drilled access point to inspect pipe runs, floor voids and wall cavities without full opening up. Used where visual confirmation of the leak source is required before committing to repair.
What to avoid
Any engineer who proposes opening floors, walls or ceilings as a first step — without attempting non-invasive detection — is not using current best practice. Non-invasive methods can locate most leaks to within a few centimetres before any surface is touched. The cost of detection equipment is justified by the cost it saves in unnecessary opening up and reinstatement.
Why leak detection in London is different from anywhere else in the UK
Victorian and Edwardian pipework
London’s pre-1914 housing stock contains original lead supply pipes, early copper runs with soldered joints, and compression fittings that have been under pressure for over a century.
These materials leak differently from modern plastic pipework — slowly, at joints, often concealed within original building fabric. Lead pipes in particular develop pinhole leaks that are acoustically quiet and thermally subtle, requiring experienced operators and sensitive equipment to locate accurately.
London clay and ground movement
London clay is one of the most reactive soils in the UK — it shrinks significantly in dry summers and swells in wet winters.¹ Buried supply pipes under gardens and external walls are subject to continuous ground movement stress.
Leaks in buried pipes in London properties are often caused by clay movement cracking or displacing the pipe rather than by pipe deterioration alone. An engineer who understands London’s ground conditions diagnoses the cause correctly and advises on repair method accordingly.
Hard water and joint failure
Much of London sits in the hard to very hard water range — as confirmed by Thames Water.² Limescale deposits at compression joints and soldered connections create stress points that eventually fail.
In London properties, joint failure at limescale accumulation points is a common source of concealed leaks behind tiles, under floors and within original wall chases. An engineer who understands London’s water chemistry will identify scale-related joint failure as a likely cause and advise on inhibitor treatment alongside the repair.
Insurance and escape of water
Escape of water is one of the costliest domestic insurance claim categories in the UK — as reported by the Association of British Insurers, insurers pay out approximately £1.8 million every day on water damage claims.³
Most home insurance policies now explicitly separate trace and access cover — finding the leak — from repair cover.
Trace and access typically covers the detection fee and any damage caused to reach the pipe; the repair itself is rarely covered and remains the homeowner’s cost.
Confirm the exact scope of your cover before commissioning detection work — some policies have approved contractor lists or cover detection costs directly.
Thames Water supply pipe responsibility
The supply pipe running from where it connects to the public water main in the highway to your property is your responsibility to maintain and repair. Thames Water is responsible for the public water main only.
If a leak detection survey identifies a leak in the supply pipe between the highway and your property, the repair cost is yours — but Thames Water offers a bill credit for water wasted during a confirmed supply pipe leak.
The repair must be completed within four weeks of identification and the claim submitted within three months of the repair date. Contact Thames Water on 0800 316 9800 to notify them of a confirmed supply pipe leak.
What leak detection costs in London
London leak detection rates sit above national averages due to operating costs specific to the capital — including parking restrictions, congestion-related delays, specialist equipment costs and insurance requirements.
Typical current ranges for London leak detection work are outlined below. Actual costs vary by property type, pipe location, detection method required and access.
Always confirm the method and scope before the engineer attends. See our London Plumbing Costs Guide for the full breakdown.
| Service | Typical London range |
|---|---|
| Acoustic leak detection (supply pipe) | £200–£400 |
| Thermal imaging survey | £200–£350 |
| Tracer gas detection | £300–£500 |
| Combined detection survey (multi-method) | £400–£700 |
| Leak detection report (for insurance) | £150–£300 additional |
| Supply pipe repair (following detection) | £300–£800 |
| Concealed pipe repair — under floor | £400–£1,200 |
Always confirm whether the quote includes the detection report, whether repair is included or quoted separately, and whether VAT is included.
Find a verified leak detection engineer in your London borough
Every engineer below is verified before listing. Find your borough and call now.
Inner South London
- Leak Detection Greenwich
- Leak Detection Lewisham
- Leak Detection Southwark
- Leak Detection Lambeth
- Leak Detection Wandsworth
- Leak Detection Merton
Inner North London
- Leak Detection Islington
- Leak Detection Hackney
- Leak Detection Camden
- Leak Detection Haringey
- Leak Detection Tower Hamlets
Inner East London
- Leak Detection Newham
- Leak Detection Waltham Forest
- Leak Detection Barking & Dagenham
- Leak Detection Redbridge
- Leak Detection Havering
Inner West London
- Leak Detection Hammersmith & Fulham
- Leak Detection Kensington & Chelsea
- Leak Detection Westminster
- Leak Detection Ealing
- Leak Detection Hounslow
- Leak Detection Richmond
Outer South London
- Leak Detection Bromley
- Leak Detection Croydon
- Leak Detection Sutton
- Leak Detection Kingston
Outer North London
- Leak Detection Barnet
- Leak Detection Brent
- Leak Detection Harrow
- Leak Detection Hillingdon
- Leak Detection Enfield
Outer East London
The City
- Leak Detection City of London
Frequently Asked Questions
The four most reliable indicators are: an unexplained increase in water bills, a boiler pressure drop with no visible cause, damp patches or staining with no obvious source, and the sound of running water when everything is turned off.
Check your water meter — a reading that moves during a 30-minute period of zero usage confirms an active supply side leak. If two or more of these indicators are present, book a leak detection survey rather than waiting for surface damage to confirm the source.
Most standard home insurance policies now separate trace and access cover from repair cover. Trace and access typically covers the cost of finding the leak and any damage caused to reach the pipe — walls, floors or ceilings opened up in the process.
The repair itself is rarely covered and is usually the homeowner’s cost. Check your policy documents before booking — some insurers have approved contractor lists or will cover detection costs directly as part of a claim. A professional detection report with precise location identified by non-invasive methods is the document that supports a claim most effectively.
Tracer gas detection uses a non-toxic mixture of nitrogen and hydrogen — typically 95% nitrogen, 5% hydrogen — introduced into the pipe under pressure. Hydrogen’s molecular size allows it to penetrate solid concrete, timber flooring and most tile types, making it effective under underfloor heating screeds without draining the system.
The mixture is non-toxic, non-flammable and harmless to building materials. It is the most precise leak detection method available and is used where acoustic detection cannot isolate the exact location.
Yes — tracer gas detection is particularly effective under concrete floors and external hardstanding where acoustic detection may be less precise. The gas rises through concrete and is detectable at the surface within minutes of introduction.
Most concealed supply pipe leaks under London properties — including those under solid concrete ground floors common in post-war conversions — are locatable by tracer gas without any opening up prior to detection.
A standard acoustic survey on a typical London terrace or flat takes one to two hours. A multi-method survey — acoustic plus thermal imaging or tracer gas — takes two to four hours depending on property size and pipe layout.
The engineer should provide a written report with the confirmed leak location before leaving. If they cannot confirm a location on the day, ask what additional steps are required and what the next cost stage is before agreeing to proceed.
Related services
Burst Pipes London · Emergency Plumber London · Blocked Drains London · Central Heating Repair London · General Plumbing London
Related guides
London Plumbing Costs Guide · Victorian Terrace Plumbing Guide · London Hard Water Guide · New Homeowner Plumbing Guide
Every engineer on this directory is independently checked before listing — not after something goes wrong. Insurance confirmed. Local coverage confirmed. Many offer work guarantees — check their profile before you call.
A leak behind a wall in a Hackney conversion and a supply pipe leaking under a Dulwich garden both need the same thing — an engineer who finds the source precisely before anything is opened up. Find your borough. Call now.
Find a Verified Leak Detection Engineer in Your Borough — Call Now →
¹ British Geological Survey — London clay shrink-swell hazard
² Thames Water — Hard water
³ Association of British Insurers — Escape of water claims