Boiler pressure dropping? There’s a reason.

Central Heating Leak Detection

A combi boiler that needs topping up every few days is telling you something: water is leaving the sealed system. Sometimes the culprit is internal — a failing expansion vessel or a weeping pressure relief valve. Just as often, it is a tiny leak on a heating pipe buried under a floor, silently soaking the structure every time the heating runs.

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Quick answer

A boiler losing pressure usually means a leak somewhere in the sealed heating circuit, though a faulty expansion vessel or leaking pressure relief valve should be checked first. If those are sound, an engineer isolates and pressure-tests each circuit to find where water is escaping, then confirms the source before repair.

Central heating leak detection costs in London

Job	Typical cost	Time
Expansion vessel and PRV check	£80–£150	1 hour
System pressure test and inspection	£120–£250	1–2 hours
Per-circuit isolation and testing	£150–£350	2–3 hours
Thermal imaging leak survey	£250–£500	2–4 hours
Concealed pipe trace under floors	£350–£700	half to full day

Typical UK trade cost-guide ranges, not a quote. Our detection fee is fixed and agreed at booking.

We diagnose the whole system, not just the symptom. First we rule the boiler in or out with component checks. Then we pressure-test the heating circuit, and if it fails, thermal imaging traces the hot pipework through the floors until the leak shows itself as a spreading warm bloom.

Catching a heating leak early is the difference between a small pipe repair and a rotted joist. If your boiler pressure keeps dropping, treat it as the early warning it is.

Detection visits carry a fixed fee under no find, no fee. Repairs quoted before work begins.

What you get

Full-system diagnosis: boiler components and pipework
Pressure testing per circuit to isolate the loss
Thermal imaging of heating runs under floors
Radiator valve and joint inspection
Repair by qualified plumbers on the day where possible
Reports for insurers when damage has occurred

How it works

A method, not a guess

Check the boiler first

Expansion vessel, PRV and internal components are ruled in or out before floor-level work.

Pressure-test the circuit

A controlled test confirms the heating pipework is losing water, and roughly how fast.

Trace with heat

With the system warm, thermal imaging follows every pipe run to the anomaly.

Pinpoint and repair

Acoustic confirmation, precise access, repair, retest, done.

Before you book anyone

7 things to know before you book central heating leak detection in London

An hourly rate is not a price - insist on a total figure

Firms advertising £80-£120 per hour sound cheaper than a fixed survey fee, until you learn a proper multi-method heating trace typically runs 2-5 hours. Three hours at £110 plus VAT already tops £390, and the clock keeps running if the first method fails. UK cost guides put detection anywhere from £80 to £1,600, with around £500 the norm, so open-ended hourly billing carries real downside. Before booking, ask one question: "What is the maximum I will pay if you find nothing?" A fixed detection fee agreed at booking - ours sits at £250-£450 for a typical London home - caps that risk before anyone steps through the door.

Read the no-find-no-fee small print - heating systems are often excluded

Plenty of firms wear the no-find-no-fee badge, but the terms frequently carve out exactly what you need: several providers restrict the guarantee to clean-water supply pipes and exclude central heating circuits altogether, citing rust and old leak-sealer residue. Other common catches: the full fee falls due if you decline an intrusive inspection, if access to a neighbouring flat cannot be arranged, or the guarantee only applies if you also pay them to cut the access hole. Ask the firm to confirm in writing that no-find-no-fee applies to your sealed heating system specifically - a genuine guarantee should survive that question.

Do the free boiler isolation test before paying anyone

You can narrow the fault yourself in one evening. Repressurise the system, close the flow and return valves under the boiler, and check the gauge after 8-12 hours. If pressure holds with the valves shut but drops with them open, the water is escaping into your pipework or radiators - a detection job. If it drops even when isolated, the fault is inside the boiler: often the expansion vessel, pressure relief valve or heat exchanger, which is a Gas Safe engineer's job, not a leak survey. Homeowners on UK forums have paid for both trades in the wrong order; this test costs nothing and tells you which one to call first.

Do not pay for parts before anyone has pressure tested the circuits

The classic misdiagnosis sequence goes: new pressure relief valve, then a recharged or replaced expansion vessel, sometimes even a heat exchanger - hundreds of pounds later the gauge still falls. Forum threads document homeowners 18 months into this cycle. Component swapping is guesswork unless someone has first pressure tested the heating circuits separately from the boiler to prove where the water is actually going. If an engineer proposes replacing a part, ask what test result points to that part. "It's usually this" is not a test result, and every fresh top-up you make in the meantime is feeding the real leak.

Treat leak sealer as a last resort, not a first response

Some traders squirt a chemical leak sealer into the system and leave. Tradespeople on plumbing forums put its success rate at roughly 50/50, working only on pinhole weeps, and typically lasting a year or two before the leak returns. Worse, sealant can clog the narrow waterways of modern condensing boiler heat exchangers, and several boiler manufacturers treat its use as grounds to void the warranty. It also contaminates the system, which is one reason some detection firms then refuse heating circuits under no-find-no-fee. If someone reaches for sealer before offering to locate the leak, that is a shortcut you will pay for twice.

Every top-up you do is quietly corroding the system

A daily or weekly top-up feels like a workaround, but each refill introduces fresh oxygenated water and dilutes the corrosion inhibitor protecting your radiators and boiler. Over months this breeds rust and sludge, shortens boiler life and can turn one small pipe leak into several. Heating engineers generally treat more than one or two top-ups a year as evidence of an active fault. Two practical rules: log the pressure reading morning and night for a week - the pattern helps whoever investigates - and once you are topping up more than weekly, stop patching and get the leak located before the escaping water damages floors and ceilings too.

Ask what the written report contains before you book

If a hidden leak has damaged floors, ceilings or walls, your buildings insurance trace-and-access cover may reimburse detection and the cost of opening up - but loss adjusters routinely challenge thin paperwork, and forum threads show claims stalling because the "report" was two lines on an invoice. Note the cover pays for finding and accessing the leak plus making good, not the pipe repair itself, and usually requires resultant damage. Ask any firm what their report includes before booking. Ours documents cause, origin, method used, a moisture map and photographs, structured for UK loss adjusters and delivered within 48 hours.

Compare like for like

Central Heating Leak Detection Across London

Losing pressure on your boiler or spotting damp near heating pipes rarely has one obvious cause. We trace central heating leaks methodically across London, from the boiler and expansion vessel through to pipework buried under screed, so you fix the real fault rather than paying to guess. Any gas work is carried out by a Gas Safe registered engineer.

What to check	A cheap hourly quote	A one-method firm	London Leak Specialist
Per-circuit pressure testing	Often skips isolating circuits, so a slow drop gets blamed on the boiler when the loss sits elsewhere in the system.	May pressure test the whole system as one, which confirms a leak exists but not which circuit or zone is losing.	We isolate and pressure test circuits separately, narrowing the loss to a specific zone before opening any floors or walls.
Expansion vessel and PRV checked first	Rarely checks the vessel or pressure relief valve, the classic reason a system reads as leaking when nothing is actually leaking.	Focused on their single detection method, so a failed vessel or weeping PRV can be missed while they hunt for pipework leaks.	We check expansion vessel charge and the PRV first, ruling out the most common 'no leak found' cause before wider tracing.
Thermal imaging under load	Unlikely to own a calibrated thermal camera, relying on visible damp that only appears once damage is already done.	May image cold, missing warm pipe runs and small losses that only show clearly with the heating running under load.	We run thermal imaging with the system hot and under load, so warm pipe routes and hidden losses stand out against the floor.
Tracer gas under screed	Typically has no tracer gas kit, so leaks under solid floors or screed are guessed at or left unresolved.	If tracer gas is their only tool, they may apply it before cheaper checks have ruled the fault in or out.	For leaks under screed or solid floors we introduce tracer gas to the circuit and pinpoint the exact escape point.
Pricing model	An open hourly rate that looks low at first but climbs with every hour, giving little reason to work efficiently.	Usually priced around their single method, so extra visits are needed and billed if that one approach does not locate it.	We quote clear survey pricing against typical UK trade cost-guide ranges, agreed before we start so you are not surprised.
No-find-no-fee	Bills the hours regardless of outcome, so you can pay in full and still not know where the leak is.	Rarely offers a no-find guarantee, as their single method cannot cover every leak type across a heating system.	Where a survey is genuinely inconclusive we discuss a fair no-find-no-fee position, so you are not paying for guesswork.
Insurer-ready report	Leaves little more than a verbal note, which is hard to use for a trace-and-access or buildings insurance claim.	Provides a limited write-up from one method, often short on the evidence an insurer expects to see.	We document findings, images and method in a clear report you can submit to your insurer for a trace-and-access claim.

From the forums

What Londoners say on Reddit & forums

Search Reddit, MoneySavingExpert and the UK DIY forums for "boiler losing pressure" and you find the same story on repeat: months of top-ups, a parade of engineers, replaced parts, and a leak nobody has actually located. Here is what London homeowners consistently report.

On MoneySavingExpert's forum, homeowners stuck in the parts-replacement cycle

A recurring thread type: pressure has been dropping for a year or more, the heat exchanger or expansion vessel has been replaced under warranty visits, sealant has been dosed in, and the gauge still falls - with the boiler engineer and the detection firm now blaming each other. The homeowner ends up switching the heating off entirely, out of pocket and no wiser. Our take: this deadlock is almost always resolved by pressure testing each circuit in isolation, which proves whether the loss sits in the boiler or the pipework before another part is bought.

On DIYnot, tradespeople and homeowners asking whether leak detection firms are worth it

The sentiment is bluntly sceptical: contributors say they hear far more complaints than success stories, comparing parts of the industry to rising-damp surveying, and quote figures like £380 plus VAT fixed or £89 per hour for firms carrying thermal, acoustic and tracer gas kit. The scepticism is usually earned by single-method operators who scan, shrug and invoice. Our take: the criticism is fair, and the fix is structural - carry every method on every visit and tie the fee to a genuine no-find-no-fee guarantee, so a failed survey costs the firm, not the customer.

On MoneySavingExpert, homeowners confused by trace-and-access insurance wording

A common shock: an insurer refuses to send contractors because there is no visible water damage yet, even though the boiler is plainly losing pressure - one poster had already spent over £600 on plumbers and a detection visit before learning the cover only responds once damage exists, and never pays for the faulty pipe itself. Others had claims queried because the paperwork did not evidence cause and origin. Our take: read your policy's trace-and-access clause before booking anyone, photograph any staining or swelling early, and make sure the detection report is written for a loss adjuster, not just for you.

On UK plumbing forums, engineers debating leak sealer as a quick fix

Trade consensus is that sealer is a coin-flip that buys a year or two at best, only ever works on tiny weeps, and carries real risk of clogging the fine waterways in modern condensing boilers - with several noting manufacturers can void the warranty over it. Homeowners repeatedly report it holding for a day or a season before the leak returns. Our take: sealer has a narrow, last-resort role, but dosing it before the leak has been located is a bodge that contaminates the system and makes proper detection harder later.

Across Reddit and DIY forums, homeowners swapping free self-diagnosis tricks

The best community advice is refreshingly cheap: isolate the boiler at its valves overnight to see whether the loss is inside the appliance or out in the pipework, tie a strip of tissue under radiator valve joints to catch invisible weeps, and keep a morning-and-night pressure log for a week before calling anyone. Posters who did this arrived at the phone call already knowing which trade they needed. Our take: do all three - a good detection engineer will ask for exactly that history, and it can shave hours off the survey.

Questions

Asked before every booking

Why does my boiler keep losing pressure?

Either water is escaping from the sealed system or a component is mismanaging pressure. The usual suspects: a leak on the heating pipework (often hidden), a weeping radiator valve, a failed expansion vessel, or a pressure relief valve that has started passing water to the outside discharge pipe. Diagnosis means checking all four — topping up and hoping is not a strategy.

Is a small heating leak really urgent?

A leak the size of a pinhead can pass litres a day into your floor structure when the system is hot and pressurised. Timber rot, lifted flooring and ceiling damage below are the usual outcomes of waiting. Early detection is dramatically cheaper.

Do you repair as well as detect?

Yes — our engineers are plumbers first. Most heating pipe repairs happen on the same visit once the leak is exposed; anything larger is quoted clearly before we continue.

Could the leak be inside the boiler itself?

It can, which is why we check the boiler before lifting a single floorboard. Internal leaks show as corrosion or drips within the casing and are handled by a Gas Safe engineer.

How much does central heating leak detection cost in London?

Expect £250-£450 for a fixed-fee multi-method survey of a typical London home; UK-wide guides quote £80-£1,600 depending on methods, with around £500 the average. Hourly operators charge roughly £80-£120 per hour, which over a normal 2-5 hour heating trace often exceeds a fixed fee. Detection is priced separately from repair, and cutting access to the pipe is usually quoted on top - so always confirm the total before booking.

Is a boiler losing pressure an emergency?

Not usually an immediate one - a slow drop will not flood your home today. But if you are topping up more than about once a week, water is actively escaping into your building, and every refill dilutes the corrosion inhibitor and feeds oxygen into the system, corroding radiators and the boiler. Treat it as urgent within days, not months: hidden heating leaks routinely surface as ruined flooring, stained ceilings or damp walls.

Can a boiler lose pressure without a leak in the pipework?

Yes. A failed expansion vessel, a passing pressure relief valve discharging outside, a faulty filling loop or a cracked heat exchanger can all drop pressure with no wet pipework at all. A quick check: close the boiler's isolation valves overnight - if pressure still falls, the fault is inside the boiler (a Gas Safe engineer's job); if it only falls with the valves open, the leak is in the heating circuit and needs locating.

How long does central heating leak detection take?

A thorough domestic survey typically takes 2-5 hours. The sequence is usually a pressure test of each circuit to confirm and isolate the loss (about 30-60 minutes), then thermal imaging, acoustic listening and, where needed, tracer gas to pinpoint the spot - sometimes within the first hour, longer under screed floors or in larger properties. Beware anyone promising a full trace in 30 minutes or billing open-ended hours without an estimate.

Does home insurance cover central heating leak detection?

Often, through trace-and-access cover on your buildings policy. It typically pays the cost of locating the leak, opening up floors or walls to reach it, and making good afterwards - but only where the escaping water has caused damage, and it never covers repairing the pipe or boiler itself. Insurers can decline claims with weak evidence, so use a firm that issues a proper report covering cause, origin, method and photographs for the loss adjuster.

Who is responsible for a heating leak in a leasehold flat?

Generally, pipework serving only your flat is your responsibility, while communal risers and heating mains fall to the freeholder or management company - check your lease, as wording varies. If your leak damages the flat below, your buildings insurer normally handles the resulting damage claim rather than you paying the neighbour directly. Detection firms may need access to adjoining flats to trace a leak, so warn neighbours and the managing agent early.

Water going somewhere it shouldn’t?

Tell us the symptoms and your postcode. We’ll confirm the visit, the fixed detection fee and the arrival window before you commit to anything.

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