A warm patch on the floor with no radiator or known pipe run beneath it is a classic sign of a central heating pipe leaking under the floor. Hot water escaping from the pipe heats the screed or boards above it. If the boiler pressure is also dropping, treat the two together. Thermal imaging can show the leak point without lifting anything.
You walked across the kitchen in bare feet and one tile was warm. Not the whole floor, just a patch the size of a dinner plate, maybe a little bigger, and it is nowhere near a radiator. Perhaps you have also been nudging the boiler pressure back up every couple of weeks and telling yourself that is normal. On its own, a warm spot is a curiosity. With a falling pressure gauge, it is a heating pipe letting go somewhere under the floor. This guide explains why a leak feels warm, how to test it with nothing more than your feet and a bit of patience, what a thermal camera shows, and what happens to a Cornish floor if the leak is left to run.
Why a leaking heating pipe makes the floor warm
Heating pipes carry water at somewhere around 60 to 70 degrees when the boiler is running. Inside a sound pipe that heat stays mostly in the water, and a pipe buried in screed or running through a floor void warms the surface only faintly and evenly along its route. When the pipe has a pinhole or a failed joint, hot water escapes into the material around it. Wet screed, wet insulation and wet timber all conduct heat far better than dry material does, so the surface directly above the leak warms up more than the rest of the run.
That is why the patch is small and local. You are not feeling the pipe, you are feeling the wet ground around the hole. The effect is strongest on tiles, stone and laminate, which is fortunate because those are the floors we see most in Cornish kitchens, utility rooms and extensions. Carpet and underlay blunt it, so on a carpeted floor you may notice a spot that never feels cold rather than one that feels warm.
A related sign is a warm patch that comes and goes with the heating programme. Warm first thing in the morning after the heating has run, cooler by lunchtime once it has been off for a while. Underfloor heating behaves differently, because the whole floor is meant to be warm, so if you have a wet system in that room, our underfloor heating leak guide is the better starting point.
The barefoot test
Before you call anyone, spend two days gathering evidence. It costs nothing and it makes any survey quicker.
- Map the patch. Walk the room in bare feet or thin socks with the heating on, then mark the warm area with masking tape. Note whether it is round, which suggests a single escape point, or a strip, which suggests a whole pipe run showing through.
- Check it cold. Turn the heating off for a few hours and walk it again. A patch that fades when the boiler is off is heating water. A patch that stays the same could be a hot water supply pipe or something else entirely.
- Read the pressure gauge. With the system cold, most boilers should sit at about 1 to 1.5 bar. Write the reading down, then again the next morning. A drop with no radiator bleeding in between is water leaving the system.
- Sniff and listen. Get close to the floor. A faint musty smell or a hiss you can only hear with everything else silent both point the same way.
- Look at the edges. Skirting boards near the patch may show a tide mark, and laminate joints nearby may have begun to lift.
If the patch fades when the heating is off and the pressure keeps dropping, you have enough to book a central heating leak detection survey. Keep the notes. They shorten the search on the day.
Pressure drop and warm patch: reading them together
How fast the gauge falls tells you the size of the hole. The table gives the pattern we see most often, though every system is a little different.
| What you notice | Most likely cause | What to do |
|---|---|---|
| Warm patch, top up every few weeks | Pinhole corrosion on a buried copper pipe | Note readings for a week, then book a survey |
| Warm patch, top up every few days | Weeping joint or larger split under the floor | Book a survey this week, keep the heating low |
| Pressure falls to zero in hours, floor warm and damp | Failed joint or burst section | Turn the boiler off, isolate if you can, get help promptly |
| Warm patch, pressure steady | Hot water supply pipe or a pipe simply routed there | Check the hot cylinder and pipe routes before assuming a leak |
If you are not sure whether topping up counts as normal, why a boiler keeps losing pressure walks through the other causes to rule out, such as the pressure relief valve and the expansion vessel, before you assume the floor.
What thermal imaging actually shows
A thermal camera reads surface temperature and paints it as colour. Point it at a floor with the heating running and a sound pipe appears as a thin, even warm line following its route. A leak appears as a bloom: a bright area spreading out from one point on the line, often with an irregular edge where the water has soaked outward through the screed or along a joist. It is the same thing your foot felt, only measured to a fraction of a degree and across the whole room at once.
The camera has limits, and an honest survey works within them. It shows where heat is reaching the surface, not always the exact hole, because water can travel along a pipe or a joist before warming the floor above. That is why the picture is cross checked with a second method before anyone is told where to dig. An acoustic ground microphone picks up the sound of water escaping under pressure, and where the pipes are plastic or the floor is thick, tracer gas can be introduced into the drained circuit and traced to the point it surfaces. Two methods agreeing is the standard for marking a repair point. One method alone is a guess with a colour scheme.
Non-invasive detection matters most in Cornwall’s older housing. A granite or cob cottage in Bodmin or Liskeard often has a solid floor laid over whatever was there before, with heating pipes chased into it decades ago and no drawing of where they went. Lifting slate or quarry tiles on a hunch is expensive and rarely puts the hole in the first hole you make.
Suspended timber floors and solid floors behave differently
Suspended timber floors
Older cottages and many pre-war houses have boards over joists with a void beneath. A leak here drips or sprays into the void, so the warm patch is often fainter and the first sign may be a musty smell rising through the boards, or damp appearing on a wall at the bottom where the water has run to the outside edge. The void does at least give the water somewhere to go, which delays the damage to the floor itself. It does nothing for the joists, and wet joist ends against a damp Cornish stone wall are a rot problem waiting to happen.
Solid concrete and screed floors
Extensions, bungalows and most post-1960s homes have pipes buried in screed over concrete. Here the leak has nowhere to go, so the screed soaks it up and the warm patch is at its clearest. The catch is that a solid floor can hide a leak for a long time. The pressure drops, the gauge gets topped up, and nothing shows at the surface until the screed is saturated. By then the water is often tracking under the floor finish across a much wider area than the warm patch suggests.
What happens if you leave it
It is tempting to keep topping up through the winter and deal with it in spring. Here is what the water is doing in the meantime.
- Fresh water feeds corrosion. Every top up brings in oxygenated water, which speeds up corrosion inside the pipes and radiators and dilutes the inhibitor. One pinhole becomes several.
- The screed weakens. Saturated screed can crumble and lose its bond to the slab. Tiles crack and laminate swells at the joints and lifts, which is often the point a small repair turns into a new floor.
- Timber rots. Under a suspended floor, warm damp joists are ideal for wet rot. Joist ends and wall plates go first, and they are the hardest parts to replace.
- Damp climbs the walls. Water under a floor finds the base of the walls. In a cob or rubble stone wall it wicks upward, and the result is easily mistaken for rising damp and treated with the wrong fix.
- The claim gets harder. Most buildings policies cover sudden escape of water, and many include trace and access cover for the cost of finding it. Damage that has clearly built up over months, with a pressure log showing you knew, invites a gradual damage argument from the insurer. Acting on the first warm patch protects you here.
What to do while you wait for the survey
Keep the heating running at a modest setting rather than turning it off completely, unless the pressure is collapsing within hours. A cold system in a damp Cornish house does more harm than a small leak over a few days, and the survey needs the system warm to work. Do not add leak sealer. It can plug the pinhole temporarily, which hides the evidence and can foul the boiler, and it makes the leak harder to find later. Move anything valuable off the floor near the patch, lift a corner of carpet if you can to let the boards breathe, and photograph the patch and the gauge each day. Those photographs are useful for the insurance claim. Our guide on what happens during a leak detection survey covers how the day runs and what the report contains.
We provide leak detection across Cornwall, from Saltash to Penzance, and the report we leave you with marks the repair point for your plumber and sets out the cause for your insurer.
Frequently asked questions
Why does a leaking heating pipe make the floor warm?
Hot water escaping from the pipe soaks the screed, insulation or timber around the hole. Wet material conducts heat far better than dry material, so the floor directly above the leak warms more than the rest of the pipe run. The warm patch is the wet ground, not the pipe itself.
Could a warm patch on the floor be something other than a leak?
Yes. A hot water pipe routed under that spot, a heating pipe passing close to the surface, or an underfloor heating loop can all warm a floor with nothing wrong. The difference is the pressure gauge. If the boiler holds pressure and the patch is a neat line, it is probably just a pipe.
Can you find a heating leak under a solid floor without digging it up?
Usually, yes. Thermal imaging shows where heat is reaching the surface, acoustic equipment listens for the escape, and tracer gas can trace a leak on a drained circuit. The methods are cross checked so the repair point is marked to a small area before any floor is opened.
Should I turn the heating off if I think a pipe is leaking under the floor?
Only if the pressure is collapsing within hours or water is visibly coming through. Otherwise keep it running at a low setting. A warm system is easier to survey, and a cold, damp house in a Cornish winter causes its own problems. Do not keep topping up more than you need to.
Will my home insurance cover a heating pipe leaking under the floor?
Many buildings policies cover damage from an escape of water and include trace and access cover, which pays towards finding the leak and making good. The failed pipe itself is not normally covered. Check your own policy, and act early so the damage cannot be called gradual.
Find the leak before the floor comes up
If one patch of floor is warm and the boiler keeps needing a top up, we can pinpoint the escape without lifting boards on a hunch. You get a marked repair point for your plumber and an insurance-ready report.
