Gurgling radiators or cold spots? Air may be trapped in your heating system. Usually, you can resolve it easily. Learn how air enters, when to bleed the system and how to do it for boilers, hybrid and all-electric heat pumps.

How does air enter your heating system?

Air can enter during refilling, temperature changes or through small leaks. It collects at high points and prevents proper hot water circulation, leaving radiators insufficiently warm and causing gurgling.

Why is bleeding important?

Trapped air reduces efficiency: heat distributes poorly, energy use rises and unnecessary wear can occur. Bleeding restores free water circulation, an important maintenance task.

Why is proper bleeding especially important with a heat pump?

A heat pump relies on water circulation. Trapped air prevents proper operation and risks noise, faults or damage. A well-bled system improves comfort, efficiency and lifespan.

How to bleed your heating

Bleeding is straightforward, though steps vary by system. Start downstairs and work upwards: air rises, so the highest radiators trap the most. Usually, you begin in the living room.

What do you need?

• A radiator bleed key, available from hardware shops
• A cloth and/or small container to catch water
• Optional: app or portal access for a smart system

Important: whether you have a heat pump or boiler, water pressure must be correct, between 1.5 and 2 bar. Check before starting. After topping up the water, you MUST bleed the heating system.

Bleeding a boiler system

• Switch off the thermostat and let the system cool.
• Check pressure is between 1.5 and 2 bar.
• Open all radiator valves fully.
• Hold a cloth or container beneath the bleed valve.
• Use the key to turn the valve a quarter-turn open.
• Air escapes first. Close the valve when water begins to drip.
• Repeat for every radiator, working from downstairs upwards.
• Recheck pressure and top up to 1.5–2 bar if needed.
• Turn the thermostat back on and check everything heats properly.

Bleeding a hybrid heat pump system

A hybrid heat pump works with your boiler, so bleeding follows largely the same process.

• Switch off the thermostat and let the system cool.
• Check system pressure and top up to 1.5–2 bar if needed.
• Fully open all zones or radiators.
• Open any automatic air vents on the system.
• Start the air-purge programme through the app or portal, if available.
• Keep a cloth or container ready at each bleed point.
• Turn the valve a quarter-turn open with the key and let air escape.
• Close the valve as soon as water emerges.
• Work through all radiators, manifolds and any underfloor heating points, from bottom to top.
• Recheck pressure and top up if needed.
• Turn the thermostat back on and check everything heats properly.

Have a Weheat system with smart zone control? Open all zones for proper circulation. You can also start the air-purge programme through the app or portal.

Bleeding an all-electric heat pump system

For a fully electric system without a boiler, the steps differ slightly but are just as simple:

• Switch off the thermostat and let the system cool.
• Check pressure is between 1.5 and 2 bar.
• Open all zones using your smart thermostat or app.
• Open automatic air vents at the heat pump and the system’s highest point.
• Start the air-purge programme through the app or portal.
• Keep a cloth or container at each bleed point.
• Carefully open the valve with a bleed key.
• Let air escape, then close the valve as soon as water emerges.
• Repeat at radiators, underfloor heating manifold, buffer tank and hot water cylinder.
• Recheck pressure and top up if needed, then repeat the bleeding process.
• End the air-purge programme and close automatic air vents.
• Turn the thermostat back on and check everything heats properly.

Bleeding a Weheat system

A few simple steps help bleed your Weheat system properly for optimum operation. First, ensure correct pressure near the heat source, between 1.5 and 2 bar depending on installation. Check and adjust if necessary.

Open automatic vents and start the programme

Open any automatic air vents so air can start escaping. Then start the air-purge programme through the portal or app to remove trapped air faster.

Zone control and manual bleeding

If you have zone control, ensure it is activated with all relevant rooms open so water circulates properly. Then begin manual bleeding.

Visit all bleed points, including radiators, underfloor heating manifold and buffer tank and cylinder connections. Open manual vents individually until no more air escapes, then close them.

Repeat and check

Repeat if needed. Once no air escapes anywhere, stop the programme and close automatic air vents.

Test the heating programme

Finally, start a heating programme to check that everything works correctly, confirming optimum system performance.

Good maintenance means better efficiency

Annual bleeding takes little effort and makes a big difference. How often is enough? For most households, bleed the system once a year ideally at the start of heating season, in September or October, when air is most likely after months of lighter use.

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