Hot water heating systems are divided into separate zones, each zone heating a different part of the home. For each thermostat located in the home, there will be a zone valve wired to the boiler to control the flow of hot water or steam to the respective area heater. Zone valves operate electrically on 24 volts of direct current power provided by a 24-volt DC transformer located at the boiler. You can wire a boiler zone valve with the proper tools and basic electrical wiring knowledge.
Things You'll Need
Wire cutting pliers
Wire stripping pliers
Turn the boiler power supply off at the main electrical panel. Tag or otherwise mark the breaker or fuse to alert others of the work being done.
Locate the zone valve DC electrical transformer. The transformer will have a 120-volt supply line connected to it. Follow the AC power supply from the panel to the transformer if it is not readily located.
Remove the protective cover from the zone valve. The cover snaps onto place and can be removed by hand.
Cut two lengths of 18-gauge insulated copper wire using the wire cutting pliers. The wire lengths must be able to reach from the thermostat assigned to the zone valve to the valve electrical terminals.
Strip 1/2-inch from both ends of each of the 18-gauge wires with wire stripping pliers. Bend open-end loops in each end of the two wires using needle-nose pliers.
Connect the looped end of one of the two wires to the thermostat terminal that leads to the center electrode of the mercury switch bulb. The bulb is made from glass and its electrode will have a wire connected to the terminal with a screw. Tighten the terminal screw clockwise with the appropriate tip screwdriver to secure the wire to the thermostat.
Connect the other end of the wire from the thermostat to the first zone valve terminal marked "TH/TR." This terminal is on the corner of the terminal buss. Do not tighten the terminal screw at this point.
Connect the second looped end wire to the thermostat terminal that leads to the outer lead on the mercury bulb switch. Tighten the terminal screw with a screwdriver.
Connect the other end of the second wire to the center terminal on the zone valve marked "TH." Tighten the terminal screw clockwise using a screwdriver.
Cut two lengths of 18-gauge wire with the wire cutters. The length should be able to reach from the zone valve to the 24-volt DC transformer.
Strip 1/2-inch from both ends of each of the 18-gauge wires using the wire strippers. Bend open end loops in each end of the wires using needle-nose pliers.
Connect one of the wires to the first "TH/TR" terminal screw along with the wire from the center probe of the thermostat. Tighten the screw with a screwdriver.
Connect the other end of the wire to the 24-volt transformer terminal opposite the "L2" 120-volt AC terminal. Tighten the terminal screw with a screwdriver.
Connect the other wire to the "TR" terminal on the zone valve with a screwdriver.
Connect the end of the wire from the "TR" terminal on the valve to the 24-volt DC transformer opposite the "L1" AC terminal. Tighten the terminal screw with a screwdriver.
Install the zone valve cover and restore electrical power to the boiler. Remove all tags from the main electrical panel.