How do you purge air from a hot water boiler?

Homeowners can purge air from a hot water boiler by using a screwdriver or radiator key to turn the radiator valve and slowly let the air out. They should hold a cup or container under the valve, as purging air causes it to drip water.

When radiators and hot water boilers fail to heat up, the culprit is often air. Air can get trapped in the radiator, which prevents heat from distributing evenly. This is an easy problem to fix. The following process only takes a few minutes and involves minimal equipment.

1. Turn off the heating system
The heating system should be turned off before working. This keeps the heater from getting too hot during the process.
2. Locate the radiator valve on the heater
The valve is usually located at the side of the heater towards the top. It usually looks like a small screw.
3. Gather tools and supplies
Find a flat-head screwdriver or radiator key to turn the valve. Newer heaters usually have valves that open with a screwdriver, but older heaters require a key. Be sure to hold the screwdriver or key with a cloth, as air escaping from the valve can cause the metal to get hot. Use a small cup or container to trap water dripping from the valve.
4. Open the valve
Turn the screwdriver or key counter clockwise. Hold the cup under the valve while opening it.
5. Let the air escape
Listen for a hissing sound. This means that air is bleeding from the valve. Leave the valve open until the hissing sound stops and water starts dripping from the heater.
6. Close the valve
Turn the valve clockwise to close it. Make sure that it is tight and secure.