Zone Valve and Zoning
How zoning delivers heat only where it is called for, using valves or multiple circulators.
Safety
What it is
Zoning divides a building into areas that can be heated independently. A hydronic system does this either with a zone valve on each branch and one circulator, or with a dedicated circulator for each zone.
End switch
A set of contacts inside a zone valve that closes once the valve is fully open, telling the boiler and circulator it is safe to start.
How it works
- 1A zone thermostat calls for heat.
- 2The zone control energizes the corresponding valve motor.
- 3The valve opens and its end switch closes.
- 4The end switch tells the zone control to start the circulator and enable the boiler.
- 5When the thermostat is satisfied the valve closes and, if no other zone is calling, the circulator and boiler stop.
Some valves are heat motor driven and open slowly. Others are motorized and move quickly. Many include a manual lever to hold the valve open for service or to allow gravity flow during a power outage.
How to diagnose it
24 volts at the valve during the zone call
No voltage points to the thermostat, wiring or zone control
Whether the valve physically opens
A stuck valve or failed motor prevents flow even with power applied
Continuity across the end switch with the valve open
An open end switch means the boiler and circulator will never start for that zone
Pipe temperature downstream of the valve
Confirms whether water is actually flowing through the zone
Whether one zone heats when another calls
A valve that will not close fully allows unwanted flow and ghost heating
Tools involved
- Multimeter
- Infrared thermometer
- Zone control wiring diagram
Symptoms
Practice & Mastery
- Zone Valve and Zoning Troubleshooting Scenarios2
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