Signs of a central heating pipe leaking under the floor include a warm patch on the floor surface, a boiler that keeps needing its pressure topped up, a rising heating bill, and a faint musty smell. Solid concrete floors hide the leak for longer than suspended timber floors. Thermal imaging and acoustic listening equipment can usually pinpoint the source without lifting the floor speculatively.
A leaking heating pipe under a floor rarely announces itself. There is no tap left running and often no puddle, just a boiler that seems to need topping up more often than it used to, or one patch of floor that feels oddly warm underfoot. This guide covers the signs worth paying attention to, why suspended timber and solid concrete floors behave differently, and what actually happens during a non-invasive survey. For the wider diagnostic picture, see our guide to how to find a leak in a central heating system.
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Warm patches: the clearest sign
Central heating water runs hot, so a central heating pipe leaking under the floor often shows up first as a patch of flooring that feels noticeably warmer than the rest of the room, even though no radiator or pipe run is supposed to be directly underneath it. On tiled or laminate floors this can be easy to feel with bare feet, particularly first thing in the morning before the whole house has warmed up. On carpeted floors it is more subtle and can be mistaken for a draught-free spot rather than a symptom.
The patch is usually localised rather than spread across the whole room, because the heat is radiating up from a specific point where water is escaping, not from the pipe run in general. If you can trace a warm patch to somewhere heating pipework is known to cross, that is a strong indicator worth acting on.
Pressure drop timing: slow leak vs sudden loss
How quickly your boiler pressure falls tells you something about the size of the leak. A pinhole leak, often caused by pitting corrosion in copper pipework, tends to lose pressure gradually, so you might only notice the gauge creeping down over several days or a couple of weeks. A larger split, a failed joint or a fitting that has come apart under pressure loses water much faster, sometimes dropping the system to zero within hours.
If you are regularly topping up the filling loop and are not sure whether that is normal, our guide to how to increase boiler pressure covers the correct process and the target range, alongside when repeated top-ups stop being routine.
| Pattern | Likely leak size | What to do |
|---|---|---|
| Top-up needed every few weeks | Small, slow leak (for example a pinhole) | Monitor for a warm patch or smell, and book a survey if it continues |
| Top-up needed every few days | Moderate leak | Check visible pipework first, then arrange a non-invasive survey |
| Pressure falls to zero within hours | Larger leak or failed joint | Shut off the system if safe to do so and get it looked at promptly |
Other signs to watch for
Alongside warm patches and pressure timing, a handful of other clues often show up together rather than alone.
- Rising heating costs without a change in how the system is used, because the boiler is working harder to maintain pressure and temperature.
- A musty or damp smell in one part of a room, particularly noticeable when the heating has been running.
- A flooring change such as laminate lifting at the joints, carpet feeling damp underfoot, or tiles sounding hollow when tapped.
- Discolouration on skirting boards or at the base of a wall nearest the suspected pipe run.
Any single sign here could have an innocent explanation. Two or three appearing together, especially alongside falling boiler pressure, is when a hidden pipe leak becomes the more likely answer.
Suspended timber floors vs solid concrete floors
The type of floor construction changes both how quickly a leak becomes obvious and how it gets investigated.
Suspended timber floors
Where there’s an accessible void beneath the boards, a leak often reveals itself sooner: a musty smell rises through the floor, or damp is visible on the underside of boards or on joists if the void can be accessed from a cellar or crawl space. This makes initial inspection more straightforward, though pinpointing the exact spot along a long pipe run still benefits from acoustic or thermal methods rather than lifting every board.
Solid concrete floors
Pipework buried in or under a concrete slab is completely hidden, so a leak can run for weeks or months before a warm patch or a change in floor covering gives it away. Water may travel sideways under the slab before finding a route upward, which means the visible warm patch is not always directly above the leak itself. This is where non-invasive detection matters most, because opening a solid floor without first narrowing the search area risks cutting into the wrong spot entirely.
What a non-invasive survey involves
A professional survey is built to locate the leak before anything gets lifted, using equipment matched to the floor type and the symptoms reported.
- Initial consultation. The engineer discusses the symptoms, when they started, and reviews boiler pressure history and any visible signs.
- Thermal imaging. A FLIR thermal camera scans the floor surface for the warm plume that hot heating water creates as it spreads through screed, insulation or timber.
- Acoustic listening. Sensitive acoustic sensors and correlators pick up the sound signature of water escaping under pressure, helping narrow the search along a pipe run.
- Tracer gas, where needed. A safe mix of 5% hydrogen and 95% nitrogen can be introduced into the system and detected at the surface with a sensitive probe, useful when thermal and acoustic readings need confirming.
- Marking and reporting. The likely leak point is marked and, where the survey is for an insurance claim, documented in a trace and access report your insurer can work from.
Our underfloor heating leak detection service and wider central heating leak detection service both use this approach, so any opening-up work that follows is targeted rather than exploratory.
What not to do while you wait
A few habits make the eventual fix harder rather than easier.
- Don’t keep lifting boards or tiles yourself to "have a look", since disturbed flooring can mask the very signs a thermal survey relies on, such as consistent surface temperature.
- Don’t ignore repeated pressure top-ups in the hope the leak seals itself. Heating leaks rarely self-resolve and usually get slowly worse.
- Don’t run the heating at full blast to "test" a warm patch. It can help confirm a suspicion, but sustained high pressure on a weak joint or pinhole can make a small leak larger.
- Do keep a simple log of when you top up the pressure and what reading you start and finish at. It gives an engineer useful context before they arrive.
Under-floor heating leaks in Cornwall & Devon homes
Many properties across Cornwall and Devon combine older solid floors with more recent heating upgrades, particularly in converted barns, cob cottages and holiday lets where pipework has been retrofitted under existing flagstone or concrete floors. That combination of an older floor structure and newer pipework crossing it is a pattern we come across regularly, and it is exactly the situation where thermal imaging earns its keep, because there is no accessible void to inspect by eye. For holiday lets left unheated between bookings, a slow leak can also go unnoticed for longer simply because nobody is in the property to feel a warm patch or notice a smell.
Frequently asked questions
How do I know if a central heating pipe is leaking under my floor?
Look for a warm patch on the floor that shouldn’t be warm, a boiler that keeps needing its pressure topped up, an unexplained rise in your heating costs, or a faint musty smell in one area. Any one of these on its own could have another cause, but two or more together, especially a warm floor patch plus falling pressure, point strongly towards a hidden pipe leak.
Can a central heating leak under the floor cause damp or mould?
Yes. A slow leak from a heating pipe can soak into floor insulation, timber joists or a concrete subfloor for weeks before it becomes visible as a stain, a lifting floor covering or a musty smell. Because the water is usually warm, it can also encourage mould growth faster than a cold water leak in the same spot.
Is a leak more likely under a suspended timber floor or a solid concrete floor?
Both can leak, but the warning signs differ. A suspended timber floor with an accessible void underneath often shows a leak sooner, through a smell or damp joists, and can be inspected by lifting boards. A solid concrete floor hides pipework completely, so a leak can run for longer before a warm patch or rising damp reading gives it away, and locating it usually needs thermal imaging or acoustic equipment rather than opening the slab speculatively.
Will my boiler pressure drop quickly if a heating pipe leaks under the floor?
It depends on the size of the leak. A pinhole leak in a heating pipe can lose pressure gradually over days or weeks, so you notice the boiler needing a top-up every so often rather than a sudden drop. A larger split or joint failure will lose pressure much faster, sometimes within hours, and is more likely to show a wet or warm patch quickly too.
Do I need to lift my floor to find a central heating leak?
Not usually as a first step. Non-invasive methods such as thermal imaging, which shows the warm plume of heating water spreading through a floor, and acoustic listening equipment, which picks up the sound of water escaping under pressure, can narrow the leak down to a small area first. Opening the floor then becomes a targeted repair rather than a search.
Is a leaking central heating pipe covered by home insurance?
Escape of water is usually covered as standard under buildings insurance, according to the Association of British Insurers. Trace and access cover, which price-comparison service Confused.com notes typically covers up to around £5,000, pays for finding the leak and making good the damage caused by the search, but not the cost of repairing the pipe itself. Check your own policy wording for the specific limits that apply.
Warm patch, falling pressure, or both? Let’s find the source
We trace central heating leaks under timber and solid floors across Cornwall & Devon using thermal imaging and acoustic equipment, so any opening-up work is targeted, not guesswork.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)