Symptoms
- Top half of the radiator feels cool or cold to the touch
- Bottom half feels warm or hot as normal
- Room heats slower than usual
Likely causes
- CommonTrapped air in the radiatorAir rises to the top of the radiator and blocks hot water from filling that space.
- PossibleSystem pressure slightly low, allowing more air to accumulateLow pressure can make air pockets more likely to form throughout the system.
- PossibleRadiator valve partially closedRestricted flow can also cause uneven heating, though usually more evenly across the radiator.
What to do
- Turn off the heating system before bleeding the radiator, and let it cool if it's hot to avoid burns.
- Locate the bleed valve, usually a small square-socket valve at one top corner of the radiator.
- Hold a cloth and small container under the valve, then use a radiator bleed key or flathead screwdriver to open it slightly.
- Listen for a hissing sound (escaping air); once it turns to a steady trickle of water, close the valve firmly.
- Check the boiler's pressure gauge afterward and top up if it dropped below the recommended range.
- Turn the heat back on and confirm the radiator now heats evenly top to bottom.
Tools and parts
- Radiator bleed key
- Cloth
- Small container
When to call a pro
Call a heating technician if bleeding doesn't fix it, if you can't find a bleed valve, or if multiple radiators need bleeding frequently.
Safety
Use caution
Let a hot radiator cool before bleeding it to avoid burns from escaping water.