No find, no fee · All London

Leak Detection London — Acoustic, Thermal & Tracer Gas

Non-invasive hidden leak detection across every London borough. If we can't pinpoint the leak using our full method suite, you pay nothing. Insurance-ready written reports as standard.

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What is professional leak detection and when does it save you money?

Every London plumber can trace a visible leak. The value of professional leak detection is in finding the leaks you can't see — the pinhole in a 15mm copper feed running 30mm below your bedroom floorboards, the split MDPE supply pipe under your Victorian front garden path, the pressure loss on your combi boiler primary that empties 20 litres a day into the void beneath your kitchen floor.

The alternative is destructive investigation. Lifting floorboards, opening walls, breaking tiles, chasing plaster — until you find the leak. On a Victorian terrace in Islington that could easily run to £3,000 in reinstatement costs before a single pipe has been repaired. Professional detection with acoustic, thermal, tracer gas and CCTV equipment finds over 96% of leaks without opening a single surface, and where destructive work is unavoidable the target zone is a 200mm square instead of an entire floor.

The second reason detection matters is insurance recognition. Every major UK household insurer will fund a “trace and access” benefit under a standard escape-of-water claim — typically £5,000 for detection and access — but only if the survey is carried out by a qualified engineer and documented to the standards the loss adjuster expects. A written report with moisture-mapping, thermal images, method log and location marked on plan is the difference between a £5,000 covered claim and a self-funded excavation.

Across AK Plumbing London's work in 2026 we have run over 480 hidden-leak surveys in every borough from Barking to Uxbridge. The single most common finding: property owners lose 4–8 weeks between first noticing a symptom (boiler pressure dropping, damp patch appearing) and calling a professional. In that gap the water damage escalates from a £180 pipe repair into a £4,000 ceiling and floor reinstatement. The economics of early professional detection are unambiguous.

Which leak detection methods do we use in London?

Every survey deploys the methods that fit the symptoms — no upselling, no unnecessary passes. Here is what each technique actually does, and where it belongs.

Acoustic listening

A parabolic microphone and floor-contact acoustic sensor pick up the sub-audible hiss of pressurised water escaping through a pinhole — usually inaudible to the human ear until you place the transducer on the tile. On concrete slab flats around Canary Wharf and Aldgate we routinely pinpoint a pinhole leak in the sub-floor 22mm copper feed to within a 200mm square, letting a chase repair replace a single tile rather than a whole bathroom floor.

The technique works best on pressurised mains (cold feed, hot feed, central heating primary), because the moving water column carries the acoustic signature. Static soil pipes and open waste pipes need a different technique — thermal imaging or camera survey.

Thermal imaging

A calibrated FLIR camera picks up the temperature differential between a warm leak plume and the surrounding wall or floor. Especially decisive on central heating primary leaks running under Victorian pine floors in Islington, Camden and Hackney terraces — the hot leak plume shows up as a bright line on the thermal image even where the pipe itself is 30mm below the floorboards.

Every leak survey using thermal imaging is done at least twice — one baseline read, one after a 30-minute pressure hold at 3 bar — so we can distinguish an active leak from a warm chase from residual solar heat on a south-facing floor.

Tracer gas

A hydrogen/nitrogen safe mix (5% H₂, 95% N₂ — non-flammable at that concentration) is injected into the system at the isolated stopcock. Hydrogen is the smallest molecule in the periodic table, so it escapes any pinhole leak and rises through the floor, wall or ceiling. We then sweep the surface with a gas-sensitive probe and mark the exact leak location.

Used exclusively on buried mains supply pipes from the boundary stopcock into the property — the classic Thames Water leak notice trigger. On a typical London Victorian terrace with a lead or MDPE feed running under a York-stone front garden path, tracer gas locates the leak within a 300mm square without lifting a single slab.

CCTV camera survey

A push-rod colour CCTV camera goes down waste pipes and drainage runs to identify blockages, misalignments, collapsed sections and root ingress. Not strictly a "leak" survey — but often the fastest way to find why a downstairs kitchen ceiling in a converted flat is dripping when nothing is on upstairs.

We record the full camera pass to USB, produce a WRC-compliant condition survey with severity ratings, and post the report to the insurance handler within 24 hours.

Moisture mapping

A calibrated pin-less capacitance meter walks the perimeter and internal walls to map moisture gradients. Distinguishes an active leak (increasing moisture upstream of the escape point) from residual damp (uniform reading, no gradient) — critical for insurance claim assessors deciding whether the loss is escape of water (covered) or long-term damp (excluded).

On a typical claim we produce a moisture-mapping annotated floor plan showing readings on a 300mm grid before and after the leak is stopped, so the loss adjuster can see the drying curve.

Leak detection cost in London — 2026 prices

Our detection call-out is charged separately from any repair, so the cost of finding a leak is independent of the cost of fixing it. Every quote is confirmed in writing before an engineer travels.

Standard residential leak survey — £250–£350. Acoustic + thermal + moisture mapping, up to 90 minutes on site, written report. Covers most internal pinhole leaks, radiator tail leaks, sink and shower waste leaks.
Complex or multi-storey leak survey — £350–£450. Ceiling drips in a converted flat where the leak may be one, two or three floors above. Involves coordinated CCTV on wastes plus acoustic on pressurised feeds. Typically 120 minutes on site.
Underground supply pipe survey (tracer gas) — £400–£550. Thames Water leak notice work. Includes tracer gas consumables, system isolation, and surface scan of the front garden or path. Written report suitable for Thames Water customer-side supply repair authorisation.
CCTV drain survey — £200–£350. Push-rod camera through waste pipes and drainage runs. Full HD recording plus WRC-compliant condition report. Suitable for insurance evidence and pre-purchase homebuyer surveys.
Repeat visit or extension — £120/hour. If a leak requires a second visit for retest after a repair, charged at hourly rate not full survey fee.

No find, no fee applies to the primary detection survey — if we can't locate the leak within the workable margin, you pay nothing. Excludes cases where the customer requires access to restricted areas we cannot enter (locked risers in blocks of flats, freeholder-only voids) — that is site access, not detection failure.

What are the signs of a hidden leak in your London property?

Most hidden leaks announce themselves 4–8 weeks before they become expensive. These are the six symptoms we ask about first on the call, and what each one typically means.

Boiler pressure keeps dropping

You top the boiler up to 1.5 bar in the morning, by the evening it is back at 0.8. Nothing visibly wet in the house. Classic sign of a pinhole leak in the central heating primary — often under a suspended timber floor in a Victorian terrace, or under a screed layer in a 1960s Barbican-style block.

Water meter ticks with all taps closed

Isolate every fixture, close the internal stop, watch the Thames Water meter dial. If the dial keeps moving you have a leak between the meter and the internal stop — that is your responsibility, not Thames Water's. Usually the underground supply pipe crossing the front garden or driveway.

Damp patch on the ceiling below a bathroom

The visible drip is almost never above the wet spot. Water tracks along a floor joist until it hits a downlight cutout, a picture rail cornice or a plasterboard joint. Acoustic + thermal work best here — resist the temptation to open the ceiling until the source is confirmed.

Unexplained water bill spike

Thames Water flags anomalous consumption above your rolling average. In a two-person Islington household the baseline is 100–130 litres/day; if you jump to 400 litres/day with no lifestyle change, something is leaking underground and running to soakaway. Tracer gas locates it fast.

Damp odour in a downstairs cupboard

Water leaks below the floor level often present first as a musty smell weeks before a visible stain appears. If the smell concentrates in the understair cupboard or a bay-window bay, we survey the primary heating and cold-feed runs immediately.

Radiator on one wall permanently cold

Sometimes not a system airlock — a slow leak on that specific radiator tail or valve has emptied the water side into the floor void. Thermal imaging along the pipework confirms in under 20 minutes.

How a leak detection visit actually works

Every leak survey follows the same five stages — from phone triage to written report. Total elapsed time between first call and report emailed to you is usually under four hours.

Free triage on the phone

You call, we ask three questions: what evidence you see, how long, and whether it is getting worse. We tell you honestly whether you need us today, this week, or whether a DIY check (water meter observation, boiler top-up test) will resolve it.

Confirm no find, no fee terms in writing

Before the engineer leaves, you get an email confirming the survey scope, the guarantee terms, and what happens if we cannot pinpoint the leak (nothing — you pay zero). No hidden clauses.

On-site — 45 to 90 minutes typical

Isolation test first (confirms there IS a live leak), then method selection (acoustic → thermal → tracer gas → CCTV in the order that best fits the symptoms). We work quietly, keep the property clean, wear overshoes, protect furniture.

Pinpoint + written report

When the leak is located we mark the exact spot, photograph it, and prepare an insurance-ready report (moisture readings, thermal images, method used, recommended remedial work).

Repair quote — separate decision

Detection and repair are separate contracts. You are never obligated to use us for the repair. We provide a fixed-price repair quote alongside the report so you can compare — many customers proceed with us because the engineer is already on site and knows exactly where the pipe is.

Standards, qualifications and insurance recognition

The single biggest gap between amateur and professional leak detection in London is documentation. Insurance loss adjusters at the major UK insurers won't authorise a trace-and-access claim on a hand-scribbled note — they need a proper written report with method log, timestamps, and readings.

Our lead engineer holds HWSS G3 unvented hot water storage certification (UK Certification Ltd, certificate 136359) and Water Regulations 1999 certification (certificate 136356), backed by a City & Guilds Level 2 NVQ Diploma in Plumbing and Heating (APL). Every survey is signed off with the engineer's certification numbers on the written report — insurers verify the credentials before authorising the trace-and-access payment.

Our public liability insurance is £5,000,000 via SiriusPoint International Insurance Corporation (UK Branch) acting through Eaton Gate MGU Ltd — policy number BE26ACTT000000018221, current period 07/05/2026 to 06/05/2027. The policy schedule includes plumbing dispatch and leak-detection survey work. We can provide the policy certificate on request as part of the detection quote — most managing agents and freehold companies require this before granting access.

Real London leak detection cases

Three recent surveys, anonymised, showing how detection actually plays out on the ground. Every case is representative of dozens of similar jobs we complete each month.

Ceiling drip in a Camden mansion block

Two-bed flat, second floor, damp patch spreading across kitchen ceiling for six weeks. Acoustic ruled out active pressurised leak. Thermal imaging showed nothing. CCTV of the flat above's bath waste picked up a hairline crack in a rubber olive seal — dripping only when the bath was drained. Repair: £180, no ceiling opened.

Underground supply pipe in a Wandsworth Victorian terrace

Thames Water leak notice — 800 litres/day unaccounted. Isolation confirmed leak was between boundary stopcock and internal stop. Tracer gas located the split MDPE feed at 45cm depth, 1.8m from the front door. Repair via keyhole excavation, one afternoon.

Central heating pinhole in a Hackney conversion

System pressure dropping 0.5 bar overnight. No visible damp. Thermal imaging on a 3-bar pressure hold revealed a hot linear signature under the pine floor of the front reception. Pinhole in a 15mm chrome-copper radiator tail replaced under a lifted single floorboard.

Leak detection across every London borough

We cover the whole of Greater London — 32 boroughs plus the M25 fringe. Response times are 60 minutes on average across Zones 1–3, 60–90 minutes for outer boroughs. Click a borough for a page tailored to local plumbing conditions.

Frequently asked questions about leak detection in London

How does "no find, no fee" actually work?

If our engineer completes a full survey using every method available (acoustic + thermal + tracer gas + CCTV where applicable) and cannot pinpoint the leak within a workable margin, you pay nothing. No hidden call-out charge, no minimum fee, no "diagnostic time" invoice. The commitment is in writing before we start. In practice we find over 96% of leaks on the first visit — but the guarantee protects you against the remainder.

How long does a leak detection visit take?

Most residential leak surveys are completed in 45–90 minutes. Underground supply pipe surveys using tracer gas take a little longer — usually 90–120 minutes — because we need to isolate the system, inject the gas, wait for pressure equalisation, and then sweep the surface systematically.

Do you provide reports for insurance claims?

Yes. Every leak survey produces an insurance-ready written report including: moisture-mapping annotated floor plan, thermal images (JPEG + CSV), method used, location marked on plan, recommended remedial work, and cost estimate. The report is prepared to the format loss adjusters at major UK insurers (Aviva, Direct Line, LV, Zurich, Allianz) expect. We can email direct to the assessor with your permission.

What does leak detection cost in London?

A standard residential leak survey starts around £250 and typically runs £300–£450 depending on complexity and access. Underground supply pipe surveys using tracer gas are usually £400–£550 because of the equipment and gas consumables involved. CCTV drain surveys are £200–£350. All prices confirmed in writing before the engineer travels — no surprises on the invoice.

Can you find leaks without damaging my floor or walls?

Yes — that is the whole point of professional leak detection. We use non-invasive methods (acoustic listening, thermal imaging, tracer gas, moisture mapping) that read the leak signature from the surface. Destructive investigation (lifting floors, opening walls) is only used when a leak is confirmed within a small area and the customer authorises access for repair. On over 90% of jobs we locate the leak without breaking a single tile.

What is the difference between acoustic and thermal imaging?

Acoustic listens for the physical noise of water escaping under pressure — best on pressurised mains, cold feed, hot feed, primary heating. Thermal imaging reads temperature differentials — best on central heating leaks (hot plume shows up against colder floor), or on cold-water leaks that have soaked into wall plaster (cooler evaporation zone). Most surveys use both methods sequentially because they answer different questions.

Do you cover the whole of London?

Yes — we work across all 32 London boroughs plus the M25 fringe. Response time is 60 minutes on average across Zones 1–3, 60–90 minutes for outer boroughs, longer only in extreme rush-hour or during severe weather. If we cannot get to you inside 90 minutes we tell you honestly on the phone.

Will you provide references from previous leak detection jobs?

Yes. We can share anonymised case studies and, with prior permission, connect you to a recent customer who commissioned a similar type of survey. Property managers and letting agents typically ask for this — happy to provide it during the initial call.

What happens if you find the leak but I use a different plumber for the repair?

Absolutely fine. Detection and repair are separate services. Our written report tells any competent plumber exactly where the leak is, how deep, and what type of pipe is involved — that is enough information for any experienced repair engineer to complete the work. You are never contractually tied to us for the follow-up repair.

Do you work with property managers and landlords on managed portfolios?

Yes — we run monthly consolidated invoicing for managed portfolios, priority dispatch on out-of-hours calls, and a dedicated account manager who knows your property list. If you manage more than 20 properties we can put together a partner arrangement with pre-agreed detection call-out terms.

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