Heating zone valves allow your boiler to heat separate parts of your home through individual thermostats. Each thermostat controls one zone valve, which in turn operates your boiler as needed to satisfy the temperature requirements. Replacing a valve does not often require draining and refilling your boiler after the repair.
Turn off the electricity to your boiler at the service switch or your main electrical panel.
Shut off the water feed to your boiler by tracing a small-diameter water pipe leading from your main water line to the boiler. Find the valve leading to the boiler and turn it to the off position. Turn off the two shutoff valves on either side of your zone valve.
Write down the position of each wire connected to the existing zone valve. For now, leave the wiring connected to the old valve.
Find the tab between the zone valve head, where the wires connect, to the zone valve body, where the piping connects. Push the tab and twist it counterclockwise to remove the valve head from the valve body. Expect a small amount of water to drip out of the body.
Let the old zone valve hang by the wires. Note the location of any wires that accidentally get disconnected from the valve.
Insert the new valve head into the old valve body. Twist it clockwise until a soft click is felt.
Disconnect each wire individually and connect it to the appropriate terminal on your new zone valve.
Restore the electricity and water to your boiler system.
Look for shutoff valves around your boiler system, especially on the piping leading into and out of your zone valve. The more you can isolate your zone valve from the rest of your water lines, the easier it is to purge the air from your pipe system. Boiler installers often have shutoff valves on either side of the zone valve to allow quick and easy replacement without the need to drain any water from your system.
To facilitate a quick repair, replace your existing zone valve with an identical model from the same manufacturer.