Boiler Leak Detection in London
A boiler that keeps losing pressure is not always a system fault. In many cases it points to a water leak, either inside the unit itself or within the heating circuit it feeds. The water may be slow enough to evaporate before it pools, which means you will not see the drip, but the pressure gauge will keep falling, and the boiler will keep locking out. That cycle does not stop until the source is identified and repaired.
Signs Your Boiler Has a Water Leak
A boiler that keeps losing pressure is not always a system fault. In many cases it points to a water leak, either inside the unit itself or within the heating circuit it feeds. The water may be slow enough to evaporate before it pools, which means you will not see the drip, but the pressure gauge will keep falling, and the boiler will keep locking out. That cycle does not stop until the source is identified and repaired.
ClearFlow uses thermal imaging and tracer gas to locate the exact point of a boiler leak without opening the unit or dismantling pipework. We introduce a safe gas mix into the heating circuit, then detect it at the surface with a calibrated electronic probe, accurate to within a few centimetres at the valve, joint or heat exchanger connection that is failing. The result is a written report your Gas Safe engineer can act on immediately, without diagnostic guesswork on their part.
Boiler manufacturers and heating engineers frequently request an independent leak detection survey before attempting internal repairs, because accurate diagnosis avoids replacing components that are not at fault. Our investigation is non-destructive, typically completed within one to two hours, and ends with a written report and photographic record of the fault location. If we cannot locate the source, you pay nothing.
- Boiler pressure gauge dropping repeatedly without explanation
- Water pooling on the floor directly beneath the boiler
- Damp patch or rust staining on pipework behind the unit
- Boiler locking out or shutting down more frequently than usual
- Musty smell or mineral deposits around the boiler casing
- Visible corrosion or white limescale residue on fittings and joints
- Topping up the system pressure more than once a month
How We Locate a Boiler Leak Without Dismantling
We review the symptoms, building type and pipe layout before selecting any equipment.
One or more methods are deployed to identify the source zone, typically narrowed to within 10–30 cm.
A second method cross-checks the result before we mark the repair point — no guesswork.
A written report with findings and photographs is issued — suitable for insurance claims.
Boiler Leak Situations We Investigate
Boiler losing pressure repeatedly
A boiler that loses pressure and needs topping up on a regular basis is the classic indicator of a slow water leak. We test the heating circuit and boiler connections under pressure to identify whether the fault is at a joint, valve, pressure relief valve discharge or within the unit itself.
Water visible beneath the boiler
A visible puddle or damp patch on the floor under the boiler suggests an active leak at a fitting, pump seal or heat exchanger. Thermal imaging identifies the temperature differential caused by escaping water before any casings are removed or any investigative work is carried out.
Boiler lockout with no fault code
Some boilers shut down as a safety response to low pressure caused by a slow leak, even when no obvious water is visible externally. We carry out a full circuit test to confirm whether pressure loss is leak-related or caused by a failing expansion vessel or pressure relief valve.
Hidden leak near the boiler
Where pipework runs behind plasterboard or through a chase close to the boiler, the source can be completely out of sight. Tracer gas permeates through plaster and screed and is detected at the surface, pinpointing the breach without the need to open walls speculatively.
Pre-repair diagnostic for the engineer
Gas Safe engineers work more efficiently when they know exactly what component is failing. Our report specifies the fault location, the method used to confirm it, and the recommended repair, giving your heating contractor a clear starting point and reducing the risk of misdiagnosis.
Combi boiler internal component leak
Combi boilers contain heat exchangers, diverter valves and plate heat exchangers that can develop micro-leaks not visible externally. We identify the affected component using thermal imaging and pressure testing, so the engineer opens only the section that needs attention.
What You Can Expect
We've been detecting hidden leaks across London for years. Every engineer is directly employed by us, DBS-checked and WaterSafe registered. We don't subcontract.
- Non-invasive investigation, no casing removed until the fault point is confirmed
- Written report handed to your Gas Safe engineer, ready to act on immediately
- No Find No Fee: if we cannot locate the source, you pay nothing
- Thermal imaging and tracer gas used together for cross-confirmed results
- Coverage across all London boroughs, with same-day attendance where possible
- Directly employed, DBS-checked engineers, no subcontractors
Trusted Across London
Absolutely quality service and what plumbers should exemplify. Turned up when they said, was kind, answered all my questions and wasn't being dodgy with anything. Skilful and efficient! Would highly recommend.
The technician arrived on time, was polite, and explained the process clearly before starting. They used advanced, non-invasive equipment to locate the leak quickly without causing any unnecessary damage to my property.
Really impressed with the service. They responded quickly and were able to accurately detect the leak without causing unnecessary damage. Professional, efficient, and clearly experienced — would highly recommend to anyone dealing with a hidden leak.
Wayne and his colleague came and within an hour found the leak deep underneath my cellar and came up with a perfect plan which made the pipe redundant and re-routed it the following morning. An excellent option if you're having a problem with a leak you cannot find.
Called Wayne Monday and he was round Tuesday evening — came out of hours to help me out. Very professional, punctual and great with communication. Fair priced too. Will definitely recommend and use again.
Contacted them and they were at the property within an hour. Honest, well priced and gave a detailed report that will likely save me hundreds of pounds. Will definitely recommend and if necessary will use again.
Wonderful efficient service — came out the same day, nothing was too much trouble. Engineers were professional and polite, explained the problem and persevered until the blockage was cleared. Would highly recommend this company.
The staff were so professional and friendly. The technician was nice and informative — he advised me the leak was outside and wrote me a report which I sent to Thames Water. In a few days they sent a repair team and found the leak. Clear Flow are great at what they do.
I received a letter from Thames Water about high water usage. Wayne arrived on time, was so professional, guided me through what he was doing and advised me of the next steps. He also wrote me a report to send to the water board. 100% recommend.
When Pressure Loss Points to a Leak
A boiler that needs its pressure topped up more than once a month is not operating normally. Pressure loss at that rate almost always indicates water is escaping from the circuit, even when there is no visible drip. The water may be evaporating on contact with the boiler casing or condensate line, or it may be leaking slowly into a void that is not easily inspected. In either case, the pressure gauge is telling you something the eye cannot see.
Not All Boiler Leaks Are the Same
Boiler leaks are not all equal in complexity. A dripping compression fitting or corroded gate valve is straightforward to locate and straightforward to fix. A micro-leak within the heat exchanger, or at the diverter valve housing inside a combi boiler, requires a different approach. Thermal imaging picks up the temperature differential where water is escaping internal surfaces. Where the leak is intermittent or very slow, tracer gas provides the precision that thermal imaging alone cannot guarantee.
Non-Destructive Detection Process
The detection process is non-destructive throughout. Our engineer will assess the boiler, its pipework connections, and the visible circuit before introducing any equipment. A thermal scan is carried out first to identify any active temperature variation. If the fault is not immediately visible, a tracer gas mix is introduced to the sealed circuit under controlled pressure, and the probe is worked methodically around every fitting, joint and connection point. The entire investigation typically takes between one and three hours.
Written Report and Next Steps
Once the fault is located, we mark the position and compile a written report with photographs. The report specifies exactly what was found, where it is, what method confirmed it, and what repair is needed. This gives your Gas Safe heating engineer a clear brief before they arrive, reducing time on the job and cutting the risk of replacing components that are not at fault. Where a home insurer is involved in covering the repair, our reports are accepted without question.
Boiler Leak Investigations
FAQs About Boiler Leak
Can't find what you're looking for? Call us on 0203 886 2316 and we'll answer on the spot.
What are the signs of a boiler water leak?
Common signs include a drop in boiler pressure, damp patches on the floor or wall around the boiler unit, rust or corrosion on the casing, and a persistent musty smell in the utility area. If your boiler is losing pressure regularly and needs topping up more than once a month, a slow internal or external leak is the most likely cause.
How do you detect a boiler leak without damaging the unit?
We use a combination of visual inspection, moisture meter readings around the boiler casing and pipework, and thermal imaging to identify temperature anomalies that indicate water tracking from a joint or heat exchanger. In most cases the source can be identified without removing panels or isolating the system.
How much does boiler leak detection cost in London?
Boiler leak detection in London typically starts from around £200 to £350, depending on the complexity of the installation and access required. We provide a fixed price before work begins. If the leak is confirmed to originate from a concealed heating pipe rather than the boiler itself, a full trace and access investigation may be recommended.
Is a boiler water leak dangerous?
A water leak from a boiler is not immediately dangerous in most cases, but it should be investigated promptly. Water near electrical components increases the risk of short circuits, and prolonged dripping can cause structural damp or corrosion to nearby pipework. If you smell gas or see any signs of combustion products, leave the property and call the National Gas Emergency line on 0800 111 999.
Can you find a boiler leak if the system is turned off?
Yes. We use moisture meters and thermal imaging which work independently of whether the system is pressurised or running. If the leak is from a joint or pipe connection, evidence of moisture migration is still detectable even when the boiler is cold. For active leaks in a running system, we may carry out a short pressurised test to confirm the source location.