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A rising water bill, a damp patch or pressure that won’t hold can mean a hidden leak — found and fixed without tearing the house apart. Find verified plumbers below, each checked before listing. Skip to verified plumbers ↓
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Jump to: Signs of a hidden leak · How leaks are traced · Whose leak is it · What it isn’t · Forest Hill specifics · Costs · Renting & council · FAQs
Signs you need leak detection
Leak detection is for the leak you can’t see. The tell-tale signs are a water bill that’s crept up for no reason, a damp patch or musty smell with no visible pipe, a boiler or system that keeps losing pressure, a warm spot on a floor over a hot-water pipe, the sound of running water when everything’s off, or a pressure-relief valve outside that keeps discharging. A hidden leak wastes water and can damage timber, plaster and finishes long before it shows — which is why tracing it early is cheaper than the repairs it causes.
How leaks are traced — without wrecking the house
The point of leak detection is to find the source precisely, so only the affected area is opened up. A specialist typically combines several non-destructive methods: acoustic listening equipment that hears water escaping under pressure; thermal imaging that spots the temperature difference of a hot-water leak or a cold damp patch; tracer gas, where a safe gas is introduced into the pipe and detected where it escapes; moisture meters to map dampness back to its source; and pressure and flow testing to confirm a leak exists and isolate which circuit it’s on. On drains, a CCTV camera survey locates a leak or break in the pipe. The result is a located leak and a targeted repair rather than guesswork and a lifted floor. A clear sequence is: confirm a leak exists, isolate the hot, cold, heating, supply or drain circuit, trace the source, then open only the targeted area. For insurers or freeholders, ask for moisture readings, photos, a leak-location note and repair notes; trace-and-access may cover opening up, but reinstatement of finishes is often a separate builder, decorator or insurer issue.
Whose leak is it?
Where the leak sits decides who’s responsible. Thames Water is responsible for the mains and the communication pipe up to your boundary; you are responsible for the supply pipe from the boundary into the home and for all internal pipes and fittings, and once a leak on your property is confirmed it’s your legal responsibility to arrange repair within four weeks. A tenant reports to the landlord. In a flat, a leak may originate in the flat above or below or in a shared stack, so establishing whose demise the leak is in — and involving the managing agent where it’s communal — is part of the job.
What leak detection isn’t
It’s worth knowing the boundaries. A pipe that’s actively burst and flooding is an emergency, not a detection job — turn off the stop tap and see Burst Pipes or Emergency Plumber. A blocked or backing-up drain is drainage work — see Blocked Drains. And rising damp or condensation isn’t always a plumbing leak at all; detection confirms whether a pipe is actually the source before anyone starts opening walls.
Forest Hill specifics
Forest Hill’s flat-heavy, hilly stock makes leak detection particularly worthwhile here. In converted and purpose-built flats, a leak showing on your ceiling often originates in the flat above, a bathroom or kitchen branch, or a shared riser, so tracing the true source — rather than assuming it’s your own pipework — avoids unnecessary work and neighbour disputes. In shopfronts with flats above, a domestic leak can appear inside a commercial unit below, so access to the flat, the shop ceiling and the managing agent may all need to be arranged. In the older Victorian and Edwardian villas, concealed pipe runs under solid floors, through rear additions and behind lath-and-plaster make a lifted-floor “search and hope” approach expensive; non-destructive tracing pays for itself. And on the hill, pressure testing helps distinguish a genuine leak from the normal pressure variation higher-up properties see.
What leak detection costs
A rough orientation to sense-check a quote — not a price list. No official pricing exists; always get it in writing.
| Job | Typical indicative range | Notes |
|---|---|---|
| Leak-detection survey (locate the source) | £150–£400 | Method depends on the leak |
| Trace + minor repair (accessible) | £250–£550 | Where repair is straightforward once found |
| Tracer-gas or thermal survey (complex) | £300–£600+ | Concealed or underground runs |
| Supply-pipe leak location (external) | £250–£600+ | Under driveways/gardens; excavation extra |
Editorial estimate only — not regulated rates, market data or a cost survey. Actual quotes vary by method, access and how concealed the leak is. Forest Hill is inside the London ULEZ, so a non-compliant van may carry the £12.50 daily charge; check the current position.
Renting or in a council home
Private tenant. Report a suspected leak or damp to your landlord or agent; Lewisham says landlords are responsible for water supply and drainage, and the council can intervene where a home is dangerous.
Council tenant. Report it to Lewisham on 0800 028 2028; a sudden flooding leak is an emergency (24/7), while a slow, contained hidden leak should go through the normal repairs route unless there is significant risk, active water escape, electrics or damage.
Why directory-listed plumbers
Leak detection is a specialism where the right equipment and method save money — and where an unchecked trader can charge to open up the wrong wall. Every plumber listed for Forest Hill is checked for identity, insurance and trading presence before going live and rechecked annually. These listing checks are administrative and don’t replace your own checks; ask to see insurance, and for water-fittings assurance look for a WaterSafe approved contractor. You contact the plumber directly: no lead fee, no per-enquiry charge, no pay-to-play ranking. Workmanship guarantees of 1, 3, 6 or 12 months are set by the plumber and aren’t insurance-backed unless stated; your Consumer Rights Act 2015 rights still apply.
Frequently asked questions
That’s a classic hidden-leak sign. A detection survey uses acoustic, thermal or tracer-gas methods to locate it before any wall or floor is opened.
The whole point of leak detection is to avoid that — non-destructive tracing locates the leak so only the affected spot is opened up.
Often. If there’s no visible drip at a radiator valve, a pressure test and leak trace find whether it’s a hidden system leak or a failed expansion vessel — see Central Heating Repair.
Usually the flat above’s or a shared stack’s. Tracing confirms the true source, and the managing agent should be involved where it’s communal. A good leak-detection visit tests before blaming a neighbour: moisture mapping, pressure checks and access to the flat above or service cupboard help prove the route.
Not usually — a slow, contained hidden leak can normally be reported and traced through the normal route, and it’s best traced calmly and properly. It becomes urgent or an emergency if there is significant risk, active water escape, damage, or water near electrics, in which case turn off the stop tap and treat it as one.
Yes — acoustic and tracer-gas methods locate an external supply-pipe leak under a drive or garden, so only the pinpointed spot needs excavating rather than the whole run.
Leak detection across Forest Hill — areas covered
Forest Hill sits within the London Borough of Lewisham, alongside Honor Oak, Sydenham, Perry Vale, Crofton Park, Brockley, Ladywell and Catford. Browse all local coverage from the Lewisham plumbers hub.
Related services in Forest Hill
Emergency Plumber · Burst Pipes · Blocked Drains · Central Heating Repair · General Plumbing
Related guides
Find Your Stop Tap · London Hard Water Guide · How to Read a Plumbing Quote · Victorian Terrace Plumbing Guide
A hidden leak is cheaper found than left — trace it precisely, fix only what’s needed, and confirm whose pipe it is before anyone opens a wall. Guarantees vary; confirm with your plumber.
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Source provenance
Routing guidance on this page is drawn from primary UK sources: Thames Water (pipe responsibility and the four-week repair duty) and the London Borough of Lewisham (private-tenant responsibilities and council repair routing), with WaterSafe as the water-fittings assurance register. Detection methods are general plumbing-engineering description; cost figures are an editorial estimate only — not regulated rates or official market data.
Last reviewed: July 2026 by Adiel Khan — SFEDI-accredited business advisor, 20+ years’ experience (South East Enterprise Ltd) and operator of VerifiedPlumbers. LinkedIn ↗
This page is checked for compliance and regulatory accuracy against the bodies cited on it — Thames Water and the London Borough of Lewisham. Source links are provided within this page where relevant.
Sources & further reading
- Thames Water — Pipe responsibility
- Thames Water — Leaks and public pipes
- London Borough of Lewisham — Repairs responsibilities
- London Borough of Lewisham — Bad housing conditions (private rented repairs)
- London Borough of Lewisham — My Repairs (emergency line, 24/7)
- WaterSafe — approved plumbing contractors