Before concrete is poured over an underfloor heating (UFH) system, the pipework must be pressure-tested. This ensures there are no leaks, weak joints, or unsealed connections that could lead to costly failure once the slab sets. Testing not only protects the system but helps stabilise pipe shape and prevent collapse during the pour. In this guide, we explain how to pressure test your underfloor heating system step-by-step before concrete is poured.
Before testing, ensure every UFH loop is connected to the manifold, including flow and return pipes. Double-check that isolators, bleed points, and valves are correctly installed. Tighten all compression fittings using the correct torque, finger-tight isn’t enough. If using push-fit or press-fit systems, check manufacturers' installation depths and seating markers. A solid mechanical connection is essential before pressure is applied.
Using a filling loop or pump, fill the system slowly with clean, cold water. Bleed each loop via its individual valve to remove air. Work methodically through each zone, allowing bubbles to escape from air vents and manifold bleeds. Never test a system that still contains significant air, false readings can occur and trapped pockets increase rupture risk under pressure. Once loops are filled, top up and ensure the system is fully primed.
Use a pressure tester or pump to raise the system pressure to 6 bar, unless the UFH supplier recommends a different value. This is higher than operating pressure to stress-test joints and fittings. Close all valves and monitor the pressure gauge. The system must be able to hold this pressure without dropping for a minimum of 1 hour for an initial test. Leave it under pressure continuously if a pour is planned shortly after.
Inspect every manifold joint, loop connection, and exposed section of pipe. Wipe joints dry and check again after 10–15 minutes for any water seepage. If pressure drops, isolate zones to pinpoint the issue. Common leak points include compression fittings that haven’t seated fully or pipes not inserted deep enough in push-fit joints. No pour should proceed until the pressure remains stable for the required period and all visible fittings are dry.
Keep the UFH system under pressure throughout the concrete pour. This helps the pipe retain its shape and rigidity during installation and makes it immediately obvious if accidental damage occurs. If a pipe gets punctured, a drop in gauge pressure will alert the crew before the concrete sets, giving a chance to halt the pour and carry out repairs. After pouring, maintain test pressure for at least 24–48 hours while the concrete cures.
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