In this how-to video, This Old House plumbing and heating contractor Richard Trethewey prevents trapped air from stopping a heating system cold in its tracks.
1. Turn off water leading to the boiler.
2. Mark the pipe for cutting, which allows the installation of the air valve.
3. Use reciprocating saw to cut out section of pipe.
4. Install copper threaded adapters to each side of the air valve.
5. Solder the air valve to the pipe.
6. Turn the water back on.
7. Switch on circulator pump to allow trapped air to escape through the valve.