Underfloor leak questions answered

The usual signs are a warm patch on a floor that should be cold, damp or lifting flooring, water at the skirting with no leak above it, a musty smell, a boiler that keeps losing pressure, a water meter that moves when every tap is off, or a hissing sound with nothing running.

One sign on its own can have other causes, such as condensation, a shower seal or a leak in the wall. A survey tests the pipes rather than guessing from the stain. See signs of a leak under the floor.

A warm patch that stays warm when the heating is off usually means hot water escaping from a heating or hot water pipe under that spot. With underfloor heating on, warm patterns are normal, so the test is whether the patch stays warm, spreads or is out of line with the loops.

If it is clean water and still coming, turn the water off at the stopcock. If the boiler pressure is dropping as well, turn the heating off. Keep electrics away from the water and take photos and meter readings before anything is moved.

Then call us on the number at the top of the page. The office is open Monday to Friday, 7:30am to 6:30pm. What to check before you call.

Yes. Water travels under floors along pipe channels, joists and the screed, so it can appear metres from the leak. On one of our jobs what looked like an underfloor heating leak was a toilet pipe, and in Battle a house full of underfloor heating turned out to have a leak on the hot supply behind a wall.

That is why the survey starts by testing which pipe is leaking before looking for where. Read the Battle case.

The finding is done from the surface: pressure testing, thermal imaging, acoustic listening, tracer gas and moisture readings. None of them needs the floor up.

To repair the pipe, the floor above the leak has to be opened, but only there. On our cases that has meant a few tiles, one strip of floorboards or a small patch of screed rather than a whole room.

An engineer is booked for the day. Some leaks are found in a couple of hours; complex systems with many circuits take longer. Reviews on this site mention both.

Pressure test gauges and isolation valves, thermal imaging cameras, acoustic ground microphones, hydrogen tracer gas and sensors, moisture meters, endoscope cameras, flow meters and leak dye. Each answers a different question, and the engineer uses them to check each other. See the equipment.

Accurate enough to open a small area, when the methods agree. Every instrument can be misled on its own: sound travels along pipes and gas follows gaps in the screed. The engineer does not recommend opening the floor until the readings point to the same place.

Someone needs to let the engineer in and be around to agree before any floor is opened. It helps to clear furniture from the rooms involved, know where the stopcock, boiler and underfloor heating manifold are, and have any drawings or photos from when the floor was laid.

Not often. When they do, it is usually a pipe damaged during building work, a joint in the floor, a fitting at the manifold, or pipe damaged by a screw or nail after the floor was laid. Several of our underfloor cases found the underfloor loops were sound and the leak was on another pipe in the same floor.

Possibly, but check the manifold first. Look for drips or white crust at the valves, actuators and connections, and at the pressure relief valve outlet. If the manifold is dry, the leak may be in a circuit, on a radiator pipe, or at the boiler.

Each underfloor circuit can be isolated at the manifold and pressure tested on its own, which tells you which loop is leaking before anyone searches the floor. Underfloor heating leaks.

We would not rely on one. A sealer may slow a very small weep, but it does not tell you where the leak is or whether water has already soaked the screed, and it can affect valves and pumps. If the pressure keeps falling, the water is going somewhere under the floor.

Electric mats and cables carry no water, so they cannot leak. A leak in a floor with electric heating will be on a water pipe running through the same floor. The heating does affect the survey: it creates warm areas and can be damaged if the floor is opened carelessly.

Many home insurance policies include trace and access cover, which pays to find the leak and open the floor to reach it. It is not always included as standard, so check your policy or call your insurer before booking.

Trace and access does not normally cover the plumbing repair itself. The damage caused by the water may be covered under a separate part of the policy. Leaks and insurance.

Yes. ADI provides a written report of the investigation, what was found and where, which you can send to your insurer or loss adjuster.

ADI’s no find, no fee terms apply to a single leak on a hot or cold water supply at one property losing at least half a litre a minute, and to water mains up to 30 metres long. They do not apply to central heating, which includes wet underfloor heating. Ask on the phone whether your job qualifies.

Often, yes. The engineers are plumbers and many of our cases were repaired on the day. Sometimes a repair has to wait, for example when the pipe needs a different fitting, the floor needs specialist lifting, or another trade has to be involved.

The engineer makes the opened area safe and tidy and, where it is a small patch, can make it good. Wet screed and subfloors usually need to dry before the final floor finish goes back, and tiles or wood flooring are normally reinstated by a flooring fitter. Ask on the phone what is included for your floor.

It depends on how long the leak ran, the floor build-up and the weather. A few days for a timber void with good airflow, weeks for a soaked screed or slab. One of our reviewers mentions two weeks for the space under their floorboards. Drying equipment speeds it up; moisture readings show when it is done.

Sometimes. Old copper in concrete can fail in more than one place, and a system that has lost pressure for months may have more than one weak point. The engineer retests after the repair, and the report notes the condition of any pipe that was exposed.