Underfloor heating (UFH) pipes can be damaged during installation, concrete pouring, or by drilling post-construction. Whether the damage is visible before the slab is poured or discovered after, prompt and correct repair is essential. Ignoring or bodging pipe repairs risks leaks, system failure, and costly floor demolition. This guide explains how to detect and repair damaged UFH pipes in a concrete floor, step-by-step, using trade-approved methods.
Start by identifying which circuit is losing pressure. Isolate loops one by one at the manifold and monitor the gauge. If the slab is already poured, use a thermal imaging camera or acoustic leak detector to pinpoint the affected area. In some cases, a damp patch or visible crack in the finish may help you triangulate the damage. Never start cutting into the slab without confirming the exact location of the fault.
Once the damaged zone is confirmed, isolate the affected circuit at the manifold and release pressure. Drain the loop using the manifold drain valve or a bleed point. If the system uses antifreeze or glycol, capture and dispose of it according to local regulations. Never attempt a heat or mechanical repair on a pressurised or wet pipe — internal moisture will compromise the repair.
Cut a controlled square or rectangular opening around the damaged area using an angle grinder with a diamond blade. Use shallow passes to avoid further damage to the pipe. Once the slab is cut, chisel out the concrete with care until the full damaged section is exposed and accessible on both sides. Clean the pipe using a dry cloth to inspect for nicks, splits, or crushed sections.
Use a pipe cutter to remove the damaged length. Make straight, square cuts to allow a proper fit for connectors. Do not use a hacksaw or blade that creates burrs or rough edges. If the pipe was kinked, extend the cut zone beyond the visible kink. Make sure you have sufficient length on either side to install a repair coupler without stress on the pipe ends.
Fit purpose-made UFH pipe repair couplers on both ends. Use brass compression or plastic push-fit connectors designed for barrier pipe. Ensure internal pipe supports are inserted if required. Tighten compression nuts evenly and test for fit. Avoid cheap plumbing connectors not rated for under-slab use — they may fail under thermal cycling or long-term pressure. All joints must be accessible and inspectable before being re-buried in concrete.
Refill the loop and pressure test to at least 6 bar. Monitor for any drops over a 1 to 2 hour period. Wipe joints dry and inspect for seepage. If no pressure loss is detected, proceed with patch repair. Keep the system pressurised during concrete reinstatement to confirm the repair is holding. If the repair leaks, replace fittings immediately and repeat the test.
Once the repair is confirmed, backfill the opening with a high-strength, fibre-reinforced concrete repair mortar. Avoid using standard cement or weak mixes. Ensure the fill fully encapsulates the pipe and couplers with no voids. Trowel flush with the floor surface and allow proper curing. If the floor is polished concrete, feather in and diamond finish the patch once cured. Refinish or reseal as needed based on the original floor treatment.
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