Non-destructive · Aquaphon & Sewerin kits · ±100mm pinpoint
Acoustic Leak Detection London
Pinpoint pressurised leaks on mains, heating, hot water and buried supply pipes — without opening walls, lifting floors or excavating driveways. Contact acoustic and ground-microphone sweep with cross-correlation on long runs.
Book an Acoustic SurveyGet a Survey Quote
Acoustic leak detection — the definitive method for pressurised leaks
Acoustic leak detection is the first-pass method for any leak on a pressurised water circuit — cold mains supply, heating primaries, hot water flow and returns, or buried MDPE supply pipes. The physics is simple. Water forcing through a leak point at pipe pressure creates a distinctive acoustic signature — a hiss between 300 Hz and 2.5 kHz on copper and steel pipework, and a sub-audible 40 Hz to 400 Hz signature on plastic MDPE. A calibrated piezo-electric contact microphone placed on the pipework picks up that signature through the pipe wall. The amplitude peaks at the point on the pipe closest to the leak, then falls off in both directions. That peak point is the pinpoint location.
What makes acoustic the default first-pass method is not the equipment — it is the fact that acoustic listening is entirely non-destructive. No lifted floors, no opened walls, no excavated driveways. On accessible pipework, a competent engineer with a modern Aquaphon or Sewerin kit will typically pinpoint a mains or heating leak within ±100mm from surface listening alone. That is small enough to cut a single 200mm access panel for the repair rather than open a whole ceiling. On buried supply pipes with a ground microphone, ±200mm on hard surfaces (concrete driveway, tarmac path) and ±300mm on softer ground (planted front garden, block paving). Cross-correlation on long runs — a 20-metre supply pipe under a driveway, a communal riser between floors — accurate to ±150mm typical.
The reason this matters commercially is the cost of the repair, not the cost of the survey. A £300 acoustic survey that pinpoints a heating leak to a specific compression joint behind a kitchen boxing means a £180 repair with a two-hour access panel cut and made good. Get the pinpoint wrong by 800mm — as happens routinely when a firm without proper acoustic equipment guesses from surface damp signs alone — and the same repair becomes £900 with a full ceiling opened, replastered and redecorated. The survey pays for itself many times over on the reinstatement saving.
Every acoustic survey we run is delivered by a Water Regulations 1999 competent engineer (UK Certification Ltd certificate 136356 issued 8 September 2025, expiry 18 August 2030) with G3 unvented hot water certification (certificate 136359, same date range). Both certificates are supplied to the loss adjuster on any insurance-backed trace-and-access survey. Public liability £5,000,000 via SiriusPoint through Eaton Gate MGU, policy BE26ACTT000000018221, period 07/05/2026 to 06/05/2027.
The five-stage acoustic survey — from isolation to pinpoint
Every acoustic survey we run follows the same disciplined sequence. Skipping any stage produces false positives — the primary reason customers end up with a “no find” outcome from firms who deploy a listening stick without proper protocol.
System isolation and pressure hold
Before any listening begins the engineer isolates the suspect circuit (cold mains, hot circuit, or heating primaries) at the closest working valve, then holds a static pressure test for 5–10 minutes. A confirmed pressure drop identifies which circuit carries the leak — acoustic listening on the wrong circuit is time wasted. Where the mains stop-tap is seized or missing (common in Victorian conversions), we fit a temporary isolation valve as part of the survey visit at no extra charge.
Contact acoustic sweep at fittings
Using a piezo-electric pipe-contact microphone (Aquaphon A200 or Sewerin AC 200), the engineer places the sensor tip on every accessible fitting, isolation valve, radiator TRV and pipe hanger along the pressurised circuit. Sound signatures at each contact point are recorded and compared. A pressurised leak radiates a characteristic hiss between 300 Hz and 2.5 kHz — the amplitude peaks at the contact point closest to the leak, then falls off on both sides.
Ground microphone sweep on buried runs
For buried supply pipes, hidden radiator drops in solid floors, or under-slab hot water runs, the engineer switches to a ground microphone (Aquaphon G200 or Fisher XLT-30). The sensor is placed on the floor surface at 20–30cm intervals and swept along the pipe run. Sub-audible leak signatures below 400 Hz appear as a rising amplitude peak — the peak point is marked on tape and re-scanned from opposite directions to confirm.
Cross-correlation on long runs
On buried supply pipes exceeding 15 metres between two accessible contact points (e.g. boundary stop-tap and internal stop-tap), a two-sensor correlator (Sewerin SeCorrPhon AC 200 or Fluid Conservation MicroCorr Touch) runs a time-of-flight calculation. The two sensors listen simultaneously at both ends of the run — the leak position along the pipe is computed from the phase difference in the leak-noise signature arriving at each sensor. Typical accuracy on cast-iron or copper mains: ±150mm.
Confirm — repeat and record
The pinpoint location is confirmed by repeating the strongest reading from a different angle, then marked on the property floor plan with GPS-style annotation (X and Y offset from a fixed reference such as a doorframe or wall corner). The engineer records the leak-noise waveform to the survey file for the written report. Every reading is timestamped and geo-referenced — a loss adjuster reviewing the report six weeks later can reproduce the finding.
When acoustic detection is the right method
Acoustic is not the answer to every leak survey. It excels on pressurised circuits. Four common London scenarios where it is the correct first-pass method:
Boiler pressure dropping — heating primaries
Combi boiler pressure falls from 1.5 bar to zero over 24–72 hours with no visible leak. Circuit isolation identifies the heating primaries as the losing circuit. Contact acoustic sweep along accessible radiator tails and pipe drops locates the leak at a compression joint hidden behind a boxed-in kitchen unit. Non-destructive pinpoint means one small access panel cut rather than the whole boxing dismantled.
Water meter turning with no taps open — cold mains supply
Thames Water leak notice or an unusual water bill spike. The internal stop-tap holds when closed, so the leak is between the boundary stop-tap and the internal stop — a buried supply run under the front garden or driveway. Ground microphone sweep along the pipe route locates the leak point ±150mm, avoiding a full excavation of the driveway.
Hot water cylinder cupboard dripping — no visible source
Damp on the airing cupboard floor with no visible drip from cylinder connections or the immersion boss. Contact acoustic on the cylinder secondary connections and cold feed identifies the leak at a hidden joint above the cylinder — often a corroded reducing tee behind the vent pipe. Contact acoustic distinguishes structural leak-hiss from cylinder expansion tick.
Basement flat ceiling damp — flat above access refused
Water staining on a basement flat ceiling. The upstairs occupier will not grant access for a full survey. Contact acoustic from below (against the ceiling void via a small inspection hole) picks up the pressurised-leak signature from the flat above, mapping the leak to a specific run of pipework. The report supports a lawful order for freeholder-authorised access to the upstairs flat.
The equipment — why kit choice determines find rate
Acoustic leak detection is one of those disciplines where the equipment budget directly determines the find rate. A cheap listening stick will find a big audible leak on a copper pipe in a quiet room. It will not find a plastic-pipe sub-audible leak, or a leak masked by traffic noise, or a long-run leak needing cross-correlation. The kit we deploy on every survey:
Aquaphon A200
Pipe-contact ground microphone for accessible pipework and buried mains. Frequency filtering 30 Hz – 4 kHz. Bluetooth headset for hands-free interpretation. Calibrated annually.
Sewerin SeCorrPhon AC 200
Two-sensor cross-correlator plus contact acoustic in one kit. Time-of-flight leak location on runs to 200 metres. Auto-correlation output with confidence-percentage flag.
Fisher XLT-30 Ground Microphone
Broadband ground microphone tuned for hard-surface (concrete, tarmac, tile) listening. Sub-audible 40–120 Hz range for buried plastic MDPE supply pipes where copper-pipe frequencies do not apply.
Fluid Conservation MicroCorr Touch
Portable colour-touchscreen cross-correlator for long-run mains. Used on trunk mains and communal supply risers in mansion blocks.
HWM Radar Sensor
Rented on demand for GPR ground-penetrating radar overlay when the pipe route is unknown or has been re-routed unrecorded.
Acoustic vs the other detection methods
Every leak survey we run starts with acoustic and adds other methods where the symptom points elsewhere. The full method-suite comparison:
| Method | Best for | Limits |
|---|---|---|
| Acoustic (this page) | Pressurised leaks — mains cold, heating primaries, hot water, buried supply pipes. | Cannot locate depressurised (drain) leaks, cannot locate leaks smaller than about 5 ml/min without help from tracer gas, less effective on plastic pipes at low pressures. |
| Thermal imaging | Hot water and heating pipe leaks in floors and walls — the leak alters the surface temperature above the pipe run. | Cannot locate cold-water leaks unless the pipe temperature is already differentiated from ambient. Poor on solid stone floors with high thermal mass. |
| Tracer gas | Buried supply pipes where acoustic finds no signal (e.g. leak smaller than acoustic threshold, or plastic MDPE at low pressure). | Requires system isolation and gas injection. Slower to set up. Requires customer consent for hydrogen/nitrogen introduction. |
| Moisture mapping | Confirming leak spread pattern once the leak is located — supports the trace-and-access insurance report. | Not a pinpoint method by itself — it locates wetness, not the leak source. |
| CCTV drain inspection | Depressurised leaks in wastes and drains — cracked bath waste, dislodged shower trap seal, root ingress on the below-ground drain. | Only applies to drainage/wastes, not to any pressurised circuit. |
Cost — acoustic leak detection surveys
Every acoustic survey is quoted in writing before the engineer travels. Prices below are indicative; exact cost depends on property size and circuit accessibility. The no find, no fee guarantee applies on every scope.
| Survey scope | Price (inc. VAT) | Includes |
|---|---|---|
| Standard residential acoustic survey (single circuit — heating or mains) | £250–£350 | System isolation, pressure hold, contact acoustic sweep, pinpoint on plan, written report within 24 hours |
| Full-circuit acoustic survey (heating + mains + hot water) | £350–£450 | All three circuits, contact and ground microphone sweep, moisture mapping cross-check, written report |
| Buried supply pipe acoustic survey (single-family home) | £300–£400 | Ground microphone sweep from boundary stop to internal stop, marked on the front elevation |
| Long-run cross-correlation survey (communal riser or trunk mains) | £450–£650 | Two-sensor correlator setup, time-of-flight leak calculation, WRC-format report for freeholder / managing agent |
| Second-opinion survey (already surveyed elsewhere with no find) | £300–£400 | Full independent method suite. Signed-off written finding regardless of previous survey outcome |
| Out-of-hours acoustic survey (evenings and weekends) | £400–£550 | Same protocol, engineer dispatched within four hours of call |
Real London acoustic surveys
Three recent acoustic surveys, anonymised. Kit, method, pinpoint and outcome.
Kentish Town Victorian terrace — heating leak behind kitchen boxing
Combi boiler pressure dropping from 1.5 to 0.4 bar over 48 hours. Isolation identified heating primaries as the losing circuit. Contact acoustic sweep along the kitchen radiator tails picked up a 900 Hz hiss peak at the join between the 15mm feed and a 22mm horizontal run inside a boxed-in unit. Single 200mm access panel cut, compression joint re-made with modern olive and jointing paste. Kitchen units back on within two hours. Repair £180 including access reinstatement.
Fulham semi-detached — buried MDPE supply pipe under driveway
Thames Water leak notice, 640 L/day loss. Internal stop-tap held on closure. Ground microphone sweep along the 8m driveway supply run identified a sub-audible peak at 3.2m from the front elevation. Cross-correlation confirmed within 100mm. Keyhole excavation exposed a fractured MDPE-to-copper coupling at 55cm depth — original 1970s installation with no thrust-block support. Repair by fusion coupling and thrust plate. Full survey and repair £820, no full driveway reinstatement required.
Marylebone mansion block — communal riser trunk mains
Third floor and above losing pressure at breakfast peak flow, freeholder unable to identify the fault after two prior surveys by other firms. Two-sensor correlation between basement plant room and roof tank room isolated the leak to a specific 4m section of copper trunk mains on the fourth-floor landing behind plasterboard. Access panel cut, corroded pinhole leak on a 42mm horizontal repaired via bronze compression sleeve. Repair completed with the block still supplied.
Acoustic leak detection across every London borough
Same acoustic method and kit across all 32 London boroughs. Click a borough for a page tailored to local plumbing patterns and property types.
Frequently asked questions about acoustic leak detection
How does acoustic leak detection actually work?
Will acoustic detection work on plastic (MDPE) supply pipes?
Can you find a leak on a heating circuit that is not currently pressurised?
What is the difference between acoustic and cross-correlation?
How accurate is the pinpoint?
Is acoustic detection safe for old copper pipes or lead mains?
Do you carry public liability insurance for leak surveys?
What certifications do your leak detection engineers hold?
Can you locate a leak that has stopped by the time you arrive?
How quickly can you attend?
Related plumbing services
Leak detection — main hub
Full explanation of every detection method and when each applies.
No find, no fee leak detection
Written guarantee terms and insurance workflow.
Hot water cylinder replacement
Cylinder leaks are a leading cause of ceiling damp in flats.
CCTV drain survey
For depressurised leaks in wastes and drains — WRC-coded reports.
Book an acoustic leak survey
Written no-find-no-fee quote before the engineer travels. Insurance-ready report within 24 hours.
Request a Survey Quote