Currently closed
Water underfloor heating installation guide
Connect each matching flow-and-return pair, then fill and purge every circuit individually through the manifold.
Once the circuits have been laid, trapped air must be removed before the completed installation is pressure tested. Manifold layouts and connectors vary, so always follow the instructions for the installed equipment.
The process at a glance
Match and connect every flow-and-return pair, close the primary isolation valves, then fill and purge each circuit separately through the manifold before pressure testing.
Pair and label every flow and return.
Prepare and connect each pipe correctly.
Isolate the manifold from the heat source.
Use the designated fill and drain points.
Keep every other flow-and-return pair closed.
Continue until discharge is steady.
Test before covering any pipework.
Prepare before starting
Gather the correct tools, connectors, hoses and project information before opening the water supply.
Identify and label
Each circuit has a flow and return end. Confirm which two pipe ends belong to each room or heating zone before making any connections.
Label every circuit clearly at the manifold. This makes filling, pressure testing, balancing and future maintenance considerably easier.
Make the connections
Use the connector specified for the pipe size, pipe construction and manifold connection. Repeat the sequence for every circuit, ensuring each flow and return is connected to the correct port.
Before introducing water
Do not fill the underfloor heating circuits through the boiler or heat source. Fill and purge through the manifold using the approved arrangement.
One loop at a time
Filling circuits separately gives the air in each loop a direct route to the drain. Opening several circuits together can let water take the easiest route while leaving air trapped elsewhere.
Air removal
After every circuit is purged
Avoid preventable problems
Most filling problems come from an incomplete flow path, unsuitable connections or treating air removal as the final system test.
Water can bypass more resistant circuits and leave trapped air. Purge one circuit at a time.
The boiler filling loop cannot purge individual floor circuits. Use the manifold fill and drain points.
Water and displaced air may enter other parts of the system instead of following the selected circuit.
An unrelated flow and return do not form the intended loop. Label and verify every pair.
Use only connectors and inserts approved for the installed pipe dimensions and manifold.
Excessive force can damage the connector, pipe or manifold. Follow the fitting instructions.
A system can fill correctly and still contain a leaking or incorrectly assembled connection.
Manifold filling questions
Clear answers about hoses, valves, actuators, trapped air and the difference between filling and commissioning.
No. Fill and purge each circuit separately while the other circuits remain closed. This ensures water passes around the full length of the selected loop and carries trapped air to the drain.
No. The underfloor heating circuits should be filled and purged through the manifold’s designated fill and drain points.
This depends on the manifold. Use the fill and drain connections identified in the manufacturer’s instructions. Do not rely on rail position, cap colour or a photograph of another model.
That depends on the actuator and manifold arrangement. They may need to be removed and replaced temporarily with manual caps so each return valve can be controlled independently. Follow the installed manifold instructions.
Trapped air can restrict circulation, create noise and prevent individual circuits from heating correctly. Each loop should produce a steady, air-free discharge before it is closed.
Confirm that both valves for the selected circuit are open, every other circuit is closed and the fill and drain valves are open. Check for kinked hoses, restricted pipework or an incorrectly assembled connector. Stop and consult a competent installer if the cause is unclear.
No. Filling and purging remove air from the circuits. Pressure testing, connection to the heat source, electrical checks, balancing and operational checks are separate commissioning stages.