Leak detection and repair

What non-invasive detection means

Non-invasive means the detection stage does no damage. Nothing is lifted, chased or drilled until the engineer can point at a specific area and say the water is coming from there. That matters most in a flat with engineered oak over screed, and in a Victorian conversion where the pipework was buried by whoever did the conversion.

The old approach was to work backwards from the damp patch, and water does not stay where it escapes. It runs along a joist, sits in screed, tracks down a party wall and appears two rooms away or a floor below. Following the stain is how people end up lifting half a floor and finding dry pipe under all of it.

The equipment and what each part is for

No single instrument finds every leak. They answer different questions, and the skill is choosing the right one for what the water is doing.

Acoustic detection listens for the leak itself. Pressurised water escaping through a small hole hisses, and that noise carries along the pipe and through the structure. A ground microphone or a contact probe picks it up, and the engineer moves along the run comparing the signal until it peaks. Acoustic work is strongest on mains and pressurised feeds, and weakest on plastic pipe in deep screed or on a gravity system with little pressure behind the water.

Thermal imaging reads surface temperature. A hot water or heating leak warms the floor above it, and the camera shows the shape of the run and the bloom where water is pooling. It works the other way round too, because cold mains water evaporating off a surface leaves it measurably cooler than the area around it. Thermal is a mapping tool rather than a pinpointing one, and it is very good at showing where not to cut.

Tracer gas handles the leaks the other methods cannot hear or see. The section is drained and a hydrogen and nitrogen mix is introduced into the pipe. The gas is far lighter than air, so it escapes at the fault and rises straight up through screed, grout and floorboards, where a surface probe finds it. This is what resolves a slow weep in buried plastic pipe, which is effectively silent and often not warm enough to image.

Moisture mapping is the dull one that saves the most floor. Meter readings taken systematically across an area show the wet edge and the direction the water is travelling, which is what decides how much flooring has to come up.

• Acoustic listening for pressurised mains and hot and cold feeds
• Thermal imaging to map hot water and heating leaks under solid floors
• Tracer gas for silent leaks in buried plastic pipe and deep screed
• Moisture meters to map the wet area and its edges
• Pressure testing to prove which circuit is losing water

Working out which system is losing water

Before any instrument comes out of the van, the engineer establishes which system is losing water. Isolate the mains at the stopcock and watch the meter: if it stops moving, the loss is on the incoming supply. Heating and unvented hot water are isolated section by section and pressure tested, so the loss shows on a gauge rather than on a ceiling. A circuit that holds pressure can be ruled out.

Not every damp patch is a plumbing leak. Perished sealant at a shower tray, a cracked waste, condensation off cold pipework in an unventilated cupboard and rainwater tracking in at a parapet all present as a ceiling stain. An engineer should tell you when the water is not ours to fix rather than open a floor to prove it.

Detection is for water you cannot see the source of. A pipe that has split and is visibly throwing water is a different job and goes straight to burst pipe repair, because there is nothing to find. If the water is running now and you want someone out rather than a survey, an emergency plumber is the right call and the detection equipment comes later if it is still needed.

If water is running now, close the main stopcock, and switch off the electricity at the consumer unit for any area where water is near a light fitting, socket or downlight. Do that before you call anyone.

Trace and access

Trace and access is the stage between finding the leak and repairing it: physically getting to the pipe. It is the part that takes the time, and the part your insurer is most likely to be interested in, because many buildings policies cover finding and reaching a leak separately from the repair itself.

Access is kept to the smallest opening that lets an engineer work: one board lifted rather than a run of them, screed cut to the size of the joint, a single tile removed where it can be lifted whole. You get told what is coming before it happens, and where a pipe runs under a kitchen unit or a staircase, the choice between opening from above or approaching from the ceiling below is yours once you know what each one means.

We record what was found and where, and photograph the opening before it is closed. If you are claiming, that is what the insurer asks for, and it is far easier to hand over than to reconstruct later.

Repair and reinstatement

What the repair looks like depends on what failed. A weeping compression joint is remade. A corroded section of copper is cut out and replaced with new pipe and properly made joints rather than patched with a clamp. A pinholed plastic barrier pipe is cut back to sound material and jointed with the correct fitting for that pipe system. A failed valve, a leaking tundish or a pressure relief line passing water is a different job again, because there the water is a symptom and the control component is the fault.

Where the run itself is at the end of its life, replacing a length is better value than repairing one hole in it, and we will say so. Copper under a solid floor that has pinholed once usually pinholes again nearby, so rerouting it somewhere accessible often saves opening the same floor twice.

Not every buried pipe has to be dug up to be repaired. Where the run is underground or under a solid floor and the fault is a joint rather than a collapsed length, the no dig methods described under pipe grouting and no dig repair can seal it from inside without opening the ground, and that is worth establishing before a driveway comes up.

Reinstatement means boards refixed, screed made up and plasterboard patched and set ready for decoration. Matching old tiles or a discontinued floor finish is not always possible, and we say that before cutting rather than after. Where a floor or wall void is genuinely wet it has to dry before it is closed permanently, because sealing damp structure in traps the moisture and it returns as mould or lifted flooring months later.

The leaks we are called to most often

On the hot water side: a leaking immersion heater boss, a weeping cylinder connection, a pressure relief valve passing to the tundish because the seat has picked up debris, and corrosion at the base of an older cylinder. Water under a cylinder is not always the cylinder, and the symptom guide on a hot water cylinder leaking sets out how to tell a fitting from a failed vessel before anyone talks about a new tank. It is worth checking whether the water is running down from a joint above. On the heating side: radiator valve glands, towel rail connections and pinholes in buried pipework. On the cold side: the mains run into the property, and the feed to an outside tap that split in a frost and went unnoticed until spring.

London adds hard water, which leaves scale that holds a worn joint together until something disturbs it, so a leak can appear days after unrelated work. And in flats above shops or above other flats, the water you can see is very often not from your own pipework.

Who pays, and what your policy actually covers

Finding a leak and repairing it are two separate costs, and in a lot of properties they land on two different people. It is worth settling that before the work starts rather than after it, because the answer often changes what you ask an engineer to do first and how much of the floor you are willing to have opened.

On the insurance side, most buildings policies treat the search and the opening up separately from the plumbing repair itself, and the wording is not standard between insurers. What your insurer means by trace and access is worth reading in your own policy document rather than assuming, because some policies pay for finding and reaching the pipe and stop there, while others also pay to make the floor good afterwards. Either way, the record of what was found and the photographs taken at the opening are what a claim is assessed on, which is why we take them as a matter of course.

In a flat, ownership of the pipe usually decides the question. A run inside your own demise is normally yours, and a riser serving the whole block is normally the freeholder or the managing agent, which is why who is responsible for a leak in a leasehold flat is a lease question before it is a plumbing one. We can establish where the water is entering from and put that in writing for you to pass on. What we cannot do is settle the liability between you and a neighbour or a freeholder, and any engineer who tells you otherwise has not read the lease either.

On our side, a plumber call out fee is a charge for attendance rather than for an outcome, so it applies whether the detection resolves in ten minutes or takes the whole visit. It is set before we attend and it does not move depending on how the search goes, which is the point of quoting it that way. The rates themselves live on the pricing page rather than in this copy, so there is one place to look and nothing to reconcile.

Before the engineer arrives

Find your stopcock and turn it off. It is usually under the kitchen sink, in a downstairs cupboard, or in a communal riser cupboard in a flat. If turning it off stops the water appearing, that tells the engineer a great deal before they get there.

Leave the affected area as it is if you can. Mopping up is sensible, but lifting flooring before detection removes the evidence that would have narrowed the search. Note when it started, whether it is constant or only when hot water runs, and whether anyone has had work done recently, including a neighbour.

Water escaping in the house does most of its damage in the first few minutes, and almost all of that is preventable from inside the property by someone who is already standing there. If water is escaping while you are reading this, the order to do things in matters more than anything else on this page. Our short guide on what to do first when water is escaping covers isolating the supply, the electrics and the affected area in the order that limits the damage.

The rate is fixed before we attend and the total depends on how long the job takes. Detection, access and repair are charged the same way, so there is no advantage to us in taking longer.