Wet Underfloor Heating Not Working
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →Do not attempt to access the underfloor heating pipes under screed or flooring. Any pipe work repairs must be done by a qualified plumber.
Wet underfloor heating (UFH) uses warm water circulating through pipes under the floor. Problems are usually in the manifold, the pump, the thermostat, or the actuators (motorised valves) — not in the pipes themselves. Most issues can be traced and resolved without breaking into the floor.
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Most likely cause & what to check
Locate the UFH manifold — usually a horizontal rail with multiple pipes connected to it, found in a utility room, cupboard, or under the stairs. Check that the flow and return temperatures shown on any gauges are correct (typically 35–55°C for UFH, much lower than radiator circuits).
Check the UFH thermostat for each zone. Ensure the setpoint is above the current room temperature and that the thermostat has power (check batteries if wireless).
Check the actuators on the manifold — these are the small motorised valves on top of each manifold port. When a zone calls for heat, the actuator should open. Press the manual override pin (usually a small button on the actuator) to force it open manually and check if flow increases.
Check the UFH pump — there is usually a dedicated circulation pump for the UFH circuit, separate from the main central heating pump. It should be warm to the touch and vibrating slightly when running. A cold, silent pump has seized or failed and needs replacing (£100–250 parts + labour).
Check the blending valve (mixing valve) on the manifold — UFH water must be blended down from the boiler temperature (70–80°C) to UFH temperature (35–50°C). If the blending valve has failed, the circuit may be getting too-cold water. Have a plumber check this.
If only one zone is cold, that actuator has likely failed. Actuators are inexpensive (£15–40) and straightforward to replace — turn off the zone, unscrew the actuator (usually just hand-tight), and fit the new one.
If the whole system is cold but the boiler is running, check that the UFH circuit has been properly balanced and that air has not become trapped in the manifold. Use the air vent screws on the manifold to bleed each circuit.
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