A zone valve is a small motorized valve that opens or shuts water flow to a heating zone based on a thermostat, letting each area warm on demand.
What A Zone Valve Does In Heating Systems
A zone valve gives you room-by-room control without adding a pump for every loop. The thermostat sends a low-voltage signal to the valve motor. As the valve opens, an internal switch proves the open position and sends a run signal to the boiler or the circulator control. When the room hits setpoint, the thermostat stops the call, the motor relaxes or a spring returns the valve to shut, and flow stops.
| Part | Job | Notes |
|---|---|---|
| Valve Body | Directs or blocks water | Brass or bronze; sweat or threaded ends |
| Actuator/Motor Head | Drives the stem or ball | Swappable on many brands |
| Return Spring | Closes when power drops | Common on “normally closed” models |
| End Switch | Signals “valve open” | Ties to boiler or pump control |
| Manual Lever | Propped-open test/bypass | Useful for purge and service |
| Transformer/Control | Supplies 24 VAC power | Often in a zone control panel |
| Thermostat | Calls for heat | Wall stat or floor sensor |
How A Zone Valve Works In Hydronic Heat
Call For Heat
The thermostat closes its contacts. Power reaches the valve motor. On spring-return designs, the motor winds against the spring. On power-open/power-close designs, the motor runs in either direction as needed.
Open Position And End Switch
When the port is fully open, a small internal switch closes. That switch feeds the boiler’s “TT” or a relay that starts the circulator. This interlock prevents the burner or pump from running with a shut valve. Taco’s control sheets describe this sequence and show the lights that indicate call, power, and end switch on their panels.
Heat Delivered, Then Shut
Hot water flows through baseboard, radiators, or tubing. The room warms up. When the setpoint is reached, the thermostat opens its contacts. The motor de-energizes. A spring snaps the valve shut, or the motor drives shut on power-close styles. The end switch opens and the boiler or pump stops.
Types Of Zone Valves For Hydronic Heat
By Power Method
Motorized spring-return. A small synchronous motor turns gears to open the port; a spring closes it when power drops. This is common in Honeywell/Resideo and Taco lines. Browse Resideo zone valves.
Power-open/power-close. The motor runs both ways. These hold position under power and can reduce wear from spring cycling in some setups.
Thermo-electric (wax motor). A heated wax element expands to push the stem open. These are quiet and compact and often used on radiant manifolds.
By Circuit Style
Two-way on/off. The most common form. The valve is either open or closed.
Three-way diverting. Directs flow between two outlets. Handy for mixing or for switching a coil between heat and cool circuits.
By Fail Position
Normally closed. Stays shut with no power; opens on call. Best for most heating loops.
Normally open. Stays open with no power; shuts on call. Used in special cases like freeze protection or gravity bypass.
By Wiring
Two-wire. Thermostat power in, end switch not provided. Often used when the boiler senses flow or when a separate flow switch exists.
Three-wire or four-wire. Separate motor leads and end-switch leads. Lets the valve prove open before firing the boiler or starting the pump. Taco and other brands label motor terminals and end-switch screws clearly on the head.
Zone Valves Vs Zone Pumps
Both methods work. Zone valves keep piping tidy with one circulator and fewer parts. Zone pumps give each loop its own curve and simple testing. Many designers use valves for baseboard homes and pumps for large or high-head loops.
Where You’ll See Zone Valves
Baseboard heat that splits by floor or wing. Radiant floor manifolds with several loops. Panel radiators with a branch per room. Fan coils that use hot water in winter and chilled water in summer. Hydronic air handlers tied to a furnace blower. Solar loops and snow-melt slabs. Anywhere a valve can meter hot or cold water to a branch, a zone valve fits the job.
Sizing And Selection Basics
Pipe size and connection. Pick a body that matches the line size, usually 1/2 to 1 inch in houses. Sweat, press, or NPT are common.
Flow rating (Cv). Match the valve to the design flow and head. Too small raises noise and pressure drop. Too large can cause ghost flow.
Fluid and temp. Check ratings for water, water-glycol, or steam, plus max temperature and pressure printed on the body.
Voltage and power draw. Most residential heads use 24 VAC, fed by a transformer or a zone panel. Some specialty heads use 120 VAC or DC. Confirm the draw so the transformer isn’t overloaded.
Fail position. Decide whether you want spring-return shut or hold-in-place. For most homes, fail-shut is preferred.
Serviceability. Many brands let you swap the head without draining the loop. That saves time later.
Steam And Chilled Water Notes
For low-pressure steam, use bodies and seats rated for steam duty and match the connection type the boiler installer prefers. Steam traps and vacuum quirks call for valves that tolerate heat and water hammer. On chilled-water jobs, insulate the body and actuator to prevent sweating that can ruin a motor head. Many heads can sit off the pipe on a short stand-off bracket, which keeps electronics away from condensation.
Wiring In Plain English
A basic panel feeds 24 VAC to each thermostat and zone valve. The thermostat closes and sends power to the valve motor leads. Once open, the end switch inside the head closes a dry contact. Those end-switch leads tie to the boiler’s call terminals or to a circulator relay. Modern zone panels simplify all of this with labeled screw terminals and lights for “call,” “power,” and “valve open.” Taco’s Zone Valve Controls handle two-, three-, and four-wire setups and make diagnostics simple.
Common Wiring Notes
Keep motor and end-switch pairs straight. Don’t gang too many valves on a small transformer. Respect the panel’s priority zone if an indirect water heater is tied in. Follow the brand’s diagram for color codes and terminal numbers.
Troubleshooting A Zone Valve
A stuck room or a cold loop doesn’t always mean the boiler failed. These quick checks list the usual suspects and help you sort valve, stat, and pump issues without guesswork.
| Symptom | Likely Cause | Quick Check |
|---|---|---|
| Room never warms | Stat open, blown fuse, dead transformer | Measure 24 VAC at panel and stat |
| Valve hums, no flow | Stuck stem or seized gear train | Move manual lever; feel pipe temp change |
| Valve opens, boiler idle | End switch not closing | Check end-switch continuity at “TT” |
| Boiler runs, loop cold | Pump off, air bound loop, closed purge | Listen for pump; bleed air at purge |
| Heat sneaks by when “off” | Valve installed backward or debris | Confirm flow arrow; clean or replace |
| Only one zone works | Shared common miswired | Trace commons to the transformer |
| Short cycling | Loose end-switch spade or bouncing stat | Reseat connectors; test stat |
| Hot head, no action | Overloaded transformer | Add VA capacity or split loads |
Care And Replacement Tips
Label each stat and valve so later work is simple. Leave an isolation valve on each branch to avoid draining the house. When purging air after work, prop the manual lever and run a slow steady stream at the purge drain until bubbles stop. Return the lever to “auto.”
On a head swap, kill power and pop the retaining clip or screws that hold the actuator. Verify that the replacement matches the model and voltage. Seat the new head, test the manual lever, then power up and run a full heat call to be sure the end switch closes as expected.
When replacing the body, match the flow arrow and keep heat time short during soldering. A heat-block paste or a wet rag on the head stub protects the internals. Clean the screen or strainer upstream if one is fitted.
When Zone Valves Are A Good Fit
One pump, many rooms. Moderate loop lengths. Quiet. Clean manifolds with tidy wiring. Those are the sweet spots for valves. They pair well with baseboard and panel rads. Radiant floors often use compact thermo-electric actuators on the manifold, which serve the same purpose as a larger valve on a branch.
When Zone Pumps Make Sense
Long runs, big head loss, or loads that vary with speed can benefit from a dedicated pump per zone. Snow-melt and large coils are common examples. Many homes do fine with valves, so pick the scheme that fits the piping plan and the gear you already own.
Helpful Brands And Documents
Installers often reach for Resideo/Honeywell V8043 and similar heads. Taco’s ZVC panels keep wiring tidy and add lights that speed up service. Brand sheets give diagrams and ratings, and they’re worth bookmarking before you start any work.