Non-Invasive Leak Detection

Thermal Imaging Leak Detection London

A thermal camera reads the temperature of a surface. It does not see water and it does not see pipe, which is a distinction worth understanding before anyone starts cutting into your floor on the strength of a colourful picture.

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How a thermal survey is priced

Job	How it is charged	Time
Imaging one room or one suspected area	Fixed detection fee, agreed on the call	Short, often the quickest option
Imaging a whole floor to follow the spread	Same fee, longer slot reserved	Depends on the footprint
Confirming the image with sound or gas before opening up	Included in the detection fee	Same visit
Attendance out of hours	Out-of-hours band, stated before travel	Day or night
Repair to whatever the camera led to	Quoted on its own once the point is marked	After you approve it

How each stage is charged, not a quote. The detection fee is fixed and agreed on the call, before an engineer travels.

What it does brilliantly is show, in seconds and without touching anything, where warm water has already spread. At two in the morning that is exactly the right question. Not yet where the hole is, but how far this has gone, which rooms are involved, and whether anything has to happen tonight at all. It is the fastest way to size up a situation in the dark.

The gap between the warm area and the actual fault is where the care goes. Water runs along joists, follows a screed layer and appears metres from where it left the pipe. So the image tells us where to concentrate, and then sound or tracer gas confirms the spot before a single board comes up.

One fixed detection fee covers the visit, including the second method used to confirm what the camera indicated. We do not price confirmation as an extra, because an unconfirmed thermal image is not a finished job. The fee and the time band are agreed before anyone travels, and repairs are quoted on their own once you can see the location.

What you get

24/7 Rapid Deployment across London, including out-of-hours and weekends.
Non-invasive detection avoids unnecessary damage to walls, floors, and ceilings.
Pinpoints exact leak location behind plaster, under tiles, or within screed.
Ideal for detecting leaks under solid concrete floors and in underfloor heating systems.
Fast diagnosis reduces overall repair time and limits water damage spread.
Clear visual evidence (thermograms) provided to show you the problem source.

How it works

A method, not a guess

What is it doing right now

The first questions are about movement and spread, not your postcode. If it is running, we talk you through the stop tap while an engineer is being assigned.

Getting the building ready

Thermal work needs a temperature difference to read. You may be asked to run the heating for a while, or to leave a room undisturbed, so the survey is not wasted.

Reading the spread

The engineer images the affected rooms and the ones next to them, following the warm path back upstream. This is fast and touches nothing at all.

Confirming before cutting

The suspected point is checked with a second method in the same visit. Only then is anything opened, and only over the confirmed spot.

Before you book anyone

Getting a thermal survey to be worth the visit

Know what the camera is actually reading

A thermal camera measures the temperature of a surface. It does not see water, it does not see pipes and it cannot look through a wall, whatever a marketing photograph implies. What it shows is the pattern left on a surface by warm water spreading underneath it. That pattern is genuinely valuable, because it tells you the extent of the problem in seconds without touching anything. It is not, on its own, a leak location, and treating it as one is how floors get opened in the wrong place.

Run the heating before the engineer arrives

Thermal imaging needs a temperature difference to read, and if there is none there is nothing to photograph. A leak on a hot water or heating circuit shows up strongly when that circuit has been running and barely at all when it has been off since morning. This matters most with underfloor heating, where a system that has been off all day will show a uniformly cold floor and an entirely wasted visit. Ask whether you should run anything beforehand, and treat it as a good sign if you are asked unprompted.

Understand why it suits a call in the small hours

The decision you need at two in the morning is narrow: does anything have to be done tonight, or can this be handled properly in daylight. Imaging answers it faster than any other method because it is instant, silent and touches nothing. It maps how far water has travelled and which rooms are involved without anyone lifting a board in the dark. Once that is known, the harder and slower work can be booked for a sensible hour instead of improvised at night.

Insist the image is confirmed before anything is cut

Water does not stay where it escaped. It runs along joists, spreads through a screed layer and appears at the lowest point it can reach, which can be a room away from the fault. So the warmest patch on the image is where water ended up, and the hole is usually upstream of it. Sound or tracer gas should confirm the spot before a board comes up. A firm that marks the bright area and reaches for a saw is about to open the wrong floor at your expense.

A cold water leak is a poor fit for this method

The whole technique rests on a temperature contrast, and cold mains leaking into an already cold floor provides very little. It can still register, since evaporation cools a surface slightly, but it is not the method to lead with. If your problem is a cold supply, a firm proposing a thermal survey as the primary approach is choosing the method that is easiest to sell rather than the one most likely to work. Listening is generally the better first move.

Check what the visit ends with, not what kit it brings

Kit lists are easy to publish and tell you very little about the outcome. The question that actually matters is what you will be holding when the engineer leaves: a marked point you can open up, or a picture and a recommendation to book something more thorough. Ask directly, and ask what happens to the fee if the answer turns out to be the second one. Checkatrade publishes a UK average of £162 for leak detection, with most jobs between £115 and £234 and a full recorded spread of £80 to £1,600, which is a useful sanity check when a short screening visit is priced like a full survey.

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What a thermal camera can and cannot settle

Thermal imaging is fast, needs no contact with anything and produces a picture that is genuinely persuasive, which is precisely the problem. A camera reads surface temperature. It shows where warm water has spread, not the hole it came out of, and those two places can be metres apart. Used as one step it is excellent. Used as the whole answer it opens floors in the wrong place.

What to check	A camera-only survey	A screening visit	How we run the call
What the image is treated as	The answer. The warmest patch is marked and the floor comes up there.	An indication, then an upsell to the survey that was needed in the first place.	A map of where water has travelled. Useful, and not yet a location. It gets confirmed before anything is cut.
Cold water leaks	Frequently missed, because there is little heat difference to photograph.	Outside what a quick screening visit can reliably pick up.	We do not lead with thermal on a cold supply. Sound or gas is the better first move and we will say so.
Conditions on the day	Ignored. The camera comes out whatever the room has been doing.	Rarely controlled for, since the visit is short by design.	Underfloor heating that has been off all day shows nothing. We will ask you to run it beforehand so the visit is not wasted.
Speed as an advantage	Sold as speed, delivered as a short visit and an early conclusion.	Genuinely quick, though quick at ruling areas in rather than out.	At two in the morning, a method that touches nothing and takes minutes is exactly right for deciding what has to happen tonight.
Confirming before opening up	Not done. The image is the evidence and the floor is the test.	A second visit, with a second method and a second fee.	Sound or tracer gas confirms the spot on the same visit, under the same fee, before anything is lifted.
What you are shown	A colourful picture with no explanation of what the colours mean.	A summary and a recommendation to book something more thorough.	The image, what it indicates, and plainly what it does not prove on its own.
Out of hours	Daytime only, which is when the imaging is least useful in a busy home.	Working hours by arrangement.	Any hour. A quiet, settled building at night gives a cleaner temperature picture than a house full of activity.

From the forums

The questions that come up when a leak starts

Thermal imaging generates more disappointed posts than any other detection method, and reading them closely the complaint is nearly always the same one: the camera did its job, and somebody treated the picture as the answer.

Posts from people who opened a floor at the brightest spot

The recurring story is a clear-looking image, an enthusiastic mark on the floor, and a hole that turns out to contain sound dry pipe. What the writer usually works out afterwards is that water had run along a joist or spread through screed before surfacing, so the warm area was downstream of the fault by a metre or more. The lesson people take away is to insist on a second method confirming the spot, and to be wary of any visit that goes from image straight to saw.

Threads about surveys carried out on a cold system

A steady trickle of posts describe an engineer arriving, imaging a floor, finding nothing and leaving with the fee. Frequently the underfloor heating had been off for a day, so there was no temperature difference to capture at all. Regulars now routinely ask new posters whether the heating was running during the visit. It is worth taking as a basic competence test: a firm that does not tell you to switch the system on beforehand is not thinking about whether your survey will work.

Discussion of cheap screening visits advertised as surveys

People compare notes on short, keenly priced visits that turn out to be a look with a camera and a recommendation to buy the proper survey. Opinion is split on whether that is a scam or simply a differently scoped product, but the practical advice is consistent: establish in advance whether the visit is expected to produce a location or an opinion. Those are different things and only one of them ends the problem.

Debates about whether thermal cameras see through walls

This comes up constantly, usually because somebody has seen an advert implying it. The answers from people who use the equipment are patient and unanimous: it reads surfaces only, and anything behind a surface is inferred from the heat pattern on the front of it. Knowing that changes how you read the image you are shown, and makes it much harder to be impressed by a picture that does not actually prove anything.

Reports from people who used imaging to decide about the night

A quieter and more positive thread type: somebody with water coming through a ceiling, an engineer who imaged the extent in a few minutes, and a decision to contain it and return in daylight. Those posts tend to end well and cheaply. The value is in using a fast non-contact method to size up a situation before committing to anything invasive, which is exactly what it is good for.

Symptoms

Symptoms thermal imaging helps diagnose

Infrared surveys map temperature anomalies from wet materials and hot heating runs. Ideal when water is tracking out of sight.

Ceiling stain with no obvious source above
Warm strip or cold patch on a solid floor
Boiler losing pressure with no visible wet spot
Underfloor heating zone colder or hotter than the rest
Damp behind kitchen or bathroom units

Prep that makes thermal imaging work

1Run heating for 30–60 minutes before arrival if a heating leak is suspected.
2Avoid opening windows that equalise room temperatures just before the survey.
3Clear furniture from the worst-affected wall or floor area.
4Mention recent sunshine on the facade. Solar gain can fake warm patches.

Thermal is a map, not the finish line

A blue or yellow blob on a thermal image shows where heat or moisture has collected, not always the exact pipe failure. We treat thermal as a screening layer and confirm with pressure tests, acoustics or tracer gas before any opening-up.

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London housing stock

Built for how London actually leaks

Housing stock across the capital fails in different ways. We match the method to the building, not a one-size survey script.

Victorian & Edwardian terraces

Original floorboards, cast-iron stacks and decades of patch repairs. We pressure-test circuits and listen through timber before any board is lifted.

Mansion blocks & conversions

Shared risers, stacked bathrooms and flat-to-flat disputes. Origin reports settle liability between leaseholders, freeholders and block insurers.

Post-war & 1970s stock

Copper branches, cold-water tanks and ageing joints. Acoustic and thermal methods locate slow drips that never show as a flood.

New-build flats & towers

Plastic pipe, underfloor heating and boosted mains. Tracer gas and thermal imaging matter more than a listening stick alone.

Questions

Thermal Imaging FAQs for London homeowners

Can a thermal camera see through my wall?

No, and any firm suggesting otherwise is overselling it. It reads the surface only. What makes it useful is that escaping water changes the temperature of the surface above it, so the camera shows the shape of the spread. That is a map of where water has been, which is genuinely valuable and is not the same as a leak location.

Will you ask me to do anything before the visit?

Possibly. The camera needs something to contrast against, so a leak on a heating or hot water circuit shows up far better when that circuit has been running. If your underfloor heating has been off all day there may be nothing to see. We would rather ask you to switch it on a few hours beforehand than turn up and waste your money.

Does it work on a cold water leak?

Less reliably, because the temperature difference is much smaller. It can still work, since cold water evaporating from a surface cools it slightly, but it is not the method we would lead with. On a cold supply we would normally start by listening and treat the camera as a way to map the spread afterwards.

Why is this good for a night call-out?

Because it is quick, silent and completely non-contact. At two in the morning the decision you need is whether this can wait until daylight, and imaging the affected rooms answers that in minutes without disturbing anyone or opening anything. Fuller work can then be booked properly for a sensible hour.

Can you find the leak from the image alone?

Sometimes, on a clear case with a strong temperature difference and a simple layout. More often the image narrows it to an area and a second method pins it down. We will not mark a spot and invite you to cut into it on the strength of a picture alone, because the warmest patch is frequently not the source.

Can thermal imaging see through my walls and floors?

No. It reads the temperature of the surface it is pointed at, nothing more. What makes it useful is that water escaping underneath changes that surface temperature, so the camera shows the shape of the spread. Everything about what is behind the surface is inference from that pattern. Any firm suggesting the camera looks through the structure is overselling what the equipment does.

Should I turn my heating on before the survey?

Usually yes, and we will tell you if so. The method needs a contrast to read, and a heating or hot water leak shows up far more clearly when that circuit has been running. With underfloor heating it is close to essential, because a floor that has been cold all day produces a uniform image and no information. A couple of hours of running beforehand can be the difference between a successful visit and a wasted one.

Does it work for finding a cold water leak?

Less reliably. The temperature difference is much smaller, so the signal is weaker and easier to lose against normal variation in the floor. It sometimes works, because evaporating water cools a surface, but it is not what we would lead with on a cold supply. Listening tends to be the better first method there, with imaging used afterwards to map how far the water has spread.

Why is imaging useful on an emergency call-out?

Because it is immediate, silent and requires no contact with anything. In the middle of the night the question is how far this has gone and whether it can wait, and imaging the affected rooms answers that within minutes without disturbing the household or opening anything up. The slower, more invasive work can then be scheduled for daylight rather than attempted badly in the dark.

Will you find the leak from the thermal image alone?

Sometimes, on a straightforward case with a strong contrast and a simple layout. More often it narrows things to an area and a second method fixes the point. We will not mark a spot and invite you to cut into it on a picture alone, because the warmest area is frequently downstream of the actual fault. Confirming first is what keeps the opening small.

Is a thermal survey non-destructive?

Entirely. Nothing is touched, drilled, lifted or drained, and there is no trace of the survey afterwards. Any damage comes later at the access stage, if opening up is needed to reach the pipe. The purpose of imaging and then confirming is to make that opening as small and as well-placed as possible rather than exploratory.

Explore the cluster

Related leak detection services & guides

Leak detection London

Hub page for multi-method surveys

Acoustic detection

Listen for pressurised pipe noise

Tracer gas

Find plastic-pipe and screed leaks

Underground leaks

Supply pipe and mains traces

Trace & access

Insurer-ready reports

Pricing

Fixed fees and no find no fee

Areas we cover

All 33 London boroughs

Leak detection guide

How methods compare

Insurance claims

Escape of water explained

London-wide

Thermal Imaging across all 33 boroughs

Same multi-method kit and fixed-fee approach from Barking to Richmond. Pick your borough for local housing detail.

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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