How to Bleed Underfloor Heating

Underfloor heating is valued for the even, gentle warmth it provides throughout a property. However, like any heating system, it requires proper maintenance to perform at its best. One of the most common issues that can affect its efficiency is trapped air in the pipes. This air prevents water from circulating smoothly, which can leave some areas of the floor colder than others and reduce overall system performance. The solution is to bleed the system, releasing the trapped air so that the water can flow properly again. Understanding how to bleed underfloor heating is important for homeowners, landlords, and property managers who want to ensure their systems continue running efficiently and safely.

Why Air Gets Trapped in Underfloor Heating

Air can become trapped in underfloor heating for several reasons. During the installation process, tiny pockets of air may remain in the pipework even after filling. Over time, dissolved air from the water supply can also separate and collect inside the system. Any leaks, repairs, or maintenance that involve draining the system can also introduce new air. This air then forms blockages that prevent warm water from flowing evenly. The result is patchy heating, unusual gurgling noises, or an overall decline in performance.

Signs That Bleeding May Be Needed

Recognising when your underfloor heating requires bleeding is essential for keeping it efficient. If you notice areas of the floor that remain noticeably cooler, this is a clear sign that circulation is restricted. Unusual noises such as bubbling or knocking in the pipes can also indicate air pockets. If the system takes much longer than usual to heat up or fails to reach the set temperature despite the boiler or heat pump working correctly, trapped air is a likely cause.

How Bleeding Works

The principle of bleeding underfloor heating is the same as bleeding a radiator: releasing trapped air so that water can circulate freely. However, the method is different because underfloor systems have longer pipe runs and are controlled by a manifold. The manifold is the central hub that distributes water to each zone or circuit of the system. Each circuit can be bled individually using valves on the manifold, ensuring that air is removed from every part of the pipework.

Preparing to Bleed an Underfloor Heating System

Before starting, it is important to turn off the heating and allow the water to cool slightly, as this prevents scalding. Access to the manifold is essential, as this is where the bleed valves are located. The system may also need topping up with water via the filling loop on the boiler to maintain correct pressure during the process. A container or hose may be used to catch the water released when bleeding. Having an adjustable spanner or radiator key may also be necessary, depending on the valve design.

Step by Step Guide to Bleeding

The process usually begins by switching off the circulation pump to stop water flowing while air is being released. The bleed valve on the first circuit is then opened slowly until water begins to flow out steadily without air bubbles. This indicates that the trapped air has been removed. The valve is then closed securely before moving on to the next circuit. Each loop of the system should be bled in turn to ensure complete removal of air. Once finished, the system pressure should be checked and topped up if required. The circulation pump can then be switched back on and the heating restarted.

Professional Help and Safety Considerations

Although bleeding underfloor heating can be carried out by confident homeowners, many prefer to hire a professional heating engineer, especially if the system is large, complex, or linked to a heat pump. Incorrect handling can lead to water leaks, damage to valves, or imbalanced circuits. Professionals not only ensure air is removed but can also check for other issues such as blockages, pump problems, or poor system balancing that may affect performance. For landlords, ensuring heating systems are kept in good working order is also part of meeting legal obligations under the Housing Health and Safety Rating System.

Preventing Air Build Up in Future

While bleeding is effective, preventing air from entering the system in the first place is the best approach. Ensuring correct installation, using quality components, and fitting an automatic air vent can all help. Regular servicing of the boiler, heat pump, and underfloor heating components also reduces the risk of air build up. Maintaining the correct system pressure is another key step, as low pressure can encourage air ingress.

Common Issues After Bleeding

After bleeding, some homeowners notice pressure drops in the system. This is normal, as water lost during bleeding reduces the pressure slightly. It is important to top up the system to the manufacturer’s recommended pressure. If problems persist, such as continued cold spots or recurring air build up, there may be an underlying fault such as a leak or incorrect system design. In such cases, professional inspection is necessary to identify and correct the problem.

Final Thoughts

Bleeding underfloor heating is a straightforward but essential maintenance task that keeps the system running efficiently. By releasing trapped air, circulation improves and rooms heat more evenly. While some homeowners may feel comfortable tackling the process themselves, many benefit from professional support to ensure it is done safely and effectively. A well maintained underfloor heating system provides reliable comfort, energy efficiency, and long term performance for any property.