Can One Thermostat Control Two Zone Valves?

Can One Thermostat Control Two Zone Valves?

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Can One Thermostat Control Two Zone Valves?

Thermostat controls the temperature of your space via automated methods. The device is a mechanical or digital mechanism that monitors and controls temperatures in various places. You can use it for heating and cooling, but not cooking.

Yes! If you have a zone valve controller, wire the two zone valves to one thermostat and the end switches to control them. This will work if the thermostat has enough heat capacity to handle your total load. The zone controller can be for either hot water supply or domestic hot water or both zones in either sequence.

This is the thermostat sequenced where the end switches are only for turning the zone valves on and off from the boiler. All these are helpful features to provide more flexibility in operation.

If you have a dual voltage (U.S. and Canadian) boiler with two heat exchangers, one per zone valve set, then you can also wire in two zone valves as a direct cooling system with the thermostat controlling both units of the fan coil.

This may work with a single-voltage unit as well. You need to have a separate temperature sensor for each zone valve (with a sensor for the boiler if it’s not dual voltage) and run wires from the boiler’s temperature sensor to each zone valve.

The end switches can turn on and off the individual zone valves.

If you want any of the above features, start with the zoned set of valves and see which functions you want to work. You should always test any setup you plan to use before it works for you.

What Are these Wires on A Zone Valve?

Zone valvesWires available
Two PortsYellow/Green– connected to the metal body of the valve.

 Neutral/Blue – Internally connected to the neutral side of the motor.

Brown, Live-in – Activates the motor inside the valve. Grey – Connected to one side of a switch inside the valve. Orange – Connected to the other side of a switch inside the valve.

Three Ports (Mid-position)White, Live in 1 – Activating motor inside the valves to select either AB (or both)  

Grey, Live in 2 – Used with White wires to select outlet A only (heating)

Orange, Live Out – This is used to switch the boiler on when the valve is at position A.

Honeywell 4 Wire Zone Valve

To properly wire a Honeywell 4-wire zone valve, you will need three 18/2 cables. These cables have four wires, 18-2 being the center two. You will now use these three 18/2 cables for this zone valve’s wiring.

The first cable will go from outside the building to the wall box inside, where it’s mounted on one side of your exterior wall.

The second cable will go from the wall box directly back into another part of your building and then directly back into a junction box in your basement ceiling on this side.

The third cable will run from this junction box back into the room, where we will mount the zone valve.

The device’s wiring can get a bit complicated. The first cable is going to have three wires labeled 18-2, and they are coming out of my wall box.

This first cable will have the 18-2 in the very middle, which is white, just like its counterpart on the other end. This second cable will have a black and red wire and a white wire.

The third cable has black, white, and red wires. You can’t do anything with the cables until you’ve mounted the device by punching these holes through the drywall and then mounting the device.

Can One Thermostat Control Two Zone Valves?

Once you’ve done that, you can punch the wires into your cable.

What Does a Honeywell Zone Valve Do?

A zone valve controls the water or steam flow in a hydronic heating or cooling system. Typically, you can find it in residential and commercial buildings. Zone valves serve various functions, like temperature control, flow distribution, and protection from freezing.

These valves are popular because they enable an even heat distribution throughout a building.

You can use this for energy efficiency and comfort and to prevent the formation of “hot spots” that leads to condensation on windowsills or water damage on ceilings.

The process of zone control depends on the fact that some areas of a building require more heat than others. This can differ in the number of walls, windows, or other heat obstructions in different areas.

You can also trace it back to differences in insulation, which will cause areas with less insulation to stay colder.

Different temperatures require that different amounts of hot water reach each area. A zone valve gets installed within the system, allowing for volume control at the individual outlets (or branch lines).

This allows hot water delivery to areas that need more and less to areas that need less.

Can One Thermostat Control Two Zone Valves?

For example, an area with many windows or a high level of insulation may need 20 gallons per hour (GPH) of hot water. A zone valve will deliver 20 GPH to the branch line upon installation. Areas that don’t need as much heat might only use 10 GPH.

What Does A 2-Port Zone Valve Do?

A 2-Port zone valve controls water flow from a heating boiler to other parts of the system, such as cold-water storage tanks and unheated spaces.

One of the three actuators controls the valve: A thermostatic expansion valve, a temperature controller or timer, or an electric immersion heater.

When the valve is open, the water flows from the heating boiler to the destination and back through the zone valve. When it’s closed, there is no flow.

The time it stays open depends on the actuator that controls it and how much heat energy you need to transfer from the heating boiler to another part of the system.

Most zone valves are single-acting, meaning that they work one way only. This is important to know when replacing a defective 2-port zone valve. If the actuator goes bad, it won’t affect your other controls because they only rely on the zone valve’s one-way action.

When most zone valves are new, they have a neutral position that causes the corresponding valve to remain in the open position. This allows you to use it while new parts are being installed.

When these valves fail, they may retain this “neutral” position through a few years of operation. Doing maintenance on them later will often result in catastrophic system damage.

Do You Need a Two-Port Valve for Underfloor Heating?

Yes! You need a two-port valve installed if your central heating system and UFH run from the same boiler, enabling the boiler to run the systems separately.

These valves are available in different types, most of which rely on a live heating system run off the same heating circuit. A single valve may be sufficient if you install a dead box or has separate circuits.

However, consult with your heating engineer before proceeding. This will rely on the size of the boiler and where it is.

If you have already removed your old central boiler and installed a new UFH, you may need to upgrade your valves, depending on the installation situation.

Your installer may have used a smaller two-port valve for the original installation, and the newer, larger system may require you to install a larger two-port valve.

Other situations may also require you if there is a change in water supply direction or the existing valves are not large enough.

If your existing valves are too small for your current boiler, you will need to replace them. This is because older boilers may not be able to run more than two UFHs (even if it does, it only has a single pump). So, a larger system would not be able to function.

How To Wire 4 Wire Honeywell Zone Valves?

First, it will be necessary to determine the number of valves needed in the system. A common residential installation would use three 4-wire valves.

For example, when there is a furnace and boiler in one location and a water heater elsewhere, six 2-wire zones must provide adequate heating/cooling throughout the home.

Use a wire gauge calculator to accurately size your wire before beginning this procedure. Calculate 6 AWG for each valve circuit (4 x 6 = 24 AWG)

If the oven is in the same space as the furnace and water heater, you will need an additional 4-wire valve. Use a wire gauge calculator to accurately size your wire before beginning this procedure. Calculate 6 AWG for each valve circuit (4 x 6 = 24 AWG)

Can One Thermostat Control Two Zone Valves?

Use a wire gauge calculator to accurately size your wire before beginning this procedure. Calculate 8 AWG for each valve circuit (3 x 8 = 24 AWG)

24 gauge for the last two wires is not necessary. The 24-gauge wire will overheat and burn. Instead, you can choose to use an 18-gauge wire for each.

In this case, you will only use one 2-wire zone (22 gauge) outside the circuit that already contains a 14-wire valve (18 gauge).

Case 1: With a 14-wire valve, you need an additional 2-wire zone to provide heating in an additional room or location. You can use the same 24 AWG wire, but instead of two separate 25-foot runs, you can splice two of the wires together.

Case 2: With a 14-wire valve and no additional zones, you will only need a single 18-gauge cable run. This is because the first circuit already contains a 4-wire valve.

22-Gauge wire is generally not an acceptable choice for this application, as it’s not usually available with appropriate connectors or materials.

Using 22-gauge wire, use very short flexibility connectors or a high-strength crimp connector in the valve box. Do not use any “standard” plumbing connections for 22-gauge wire.

24-gauge wire is available, but generally, this would be too expensive for this application. It may be cheaper to buy a higher quality 8 AWG wire with connectors and cut it to length before splicing.

Why are There an Override Switch on Zone Valves?

These switches control the circulator pump either directly or through a relay. One common use is to control a circulating pump in a swimming pool, allowing the pump to run only when someone is in the water.

When you turn this switch off, water flows freely through the pool and falls into a skimmer that removes any dirt or debris.

You can install override switches on valves with a float switch setting. The override switch needs to be open to allow normal circulation.

The function of a zone valve is to control the flow of water to a location or device. Sometimes you must remove a zone pipe from service and stop the water flowing through it.

If the water is in motion, the valve may become damaged or clogged, with severe consequences.

You can use the override switch to turn off the zone pipe before it becomes damaged. Install the zone valve on a pipe to control the water through a skimmer or another device.

The zone valve is usually below the water surface. You can also use override switches in a swimming pool to stop circulation when someone is in the pool.

The “well” is the piping that connects water from a water source to your home. A typical well has many different pipes with different types of valves in them. Three valves are used in wells: conventional, shutoff, and bypass

Should Zone Valves Go on The Supply or Return?

In many installations, the zone valves are in the returns. The zone valve controls the volume of water you will heat or chill in that particular zone.

When you turn on the valve, water will flow through the pipes in that zone and either heat or cool by passing it through coils before returning to the distribution system (the region within the location of all your home’s plumbing connections).

In more complicated installations, you may need multiple valves to control how much water flows through each pipe. You need additional valves to control how much water flows through each zone.

The valves in the returns should not be closer than 30 feet or so from the zone valves. As a general rule, you should install zone valves upstream of zone pumps.

You should also install them closer to rooms needing heating or cooling (and where there will be a greater flow of water) than in zones where there is lower demand for hot water and farther from zones where there is lower demand for cold water.

Always leave valves located in the returns on the hot water side of the system, so that cold water (carrying dissolved air) coming back from the house will flow through them, allowing their temperature to equalize with that of the installation of the water.

How Much Does It Cost to Replace a Heating Zone Valve?

Heating zone valves are used to heat your house. Depending on who you ask, some can cost hundreds to thousands of dollars. This is because some people may be replacing an entire heating system or just the valves.

To know how much a replacement heating zone valve will cost you, you have to know the measurements and age of the valve.

The size of the heating zone valve you want to replace depends on your living space. The most common sizes are 6″, 8″, 10″ and 12″.

The size of each heating zone valve can be easily found by googling the model number, and it will probably say “sizing guide” or “specifications.”

This sizing guide will help you determine how much a single valve will cost. However, you don’t have to be limited to a single valve.

You can find a dual valve that heats two zones and frost-free 8″ and 12″ valves. You have to know the measurements of each valve you want to buy.

Type of RepairAmount
Faulty Circulator Pump$400 – $800
Broken ignitor$125 – $250
System Flush$200 – $500
Stopping leaks$100 – $400
Faulty zone valve$350 – $800

Do I Need to Drain the System to Change the Motorized Valve?

No! Nowadays, you can replace most actuators without draining down the system. However, if you have a thermal expansion tank installed, there is the possibility that it will need draining and refiling after changing an actuator.

You must not overfill the expansion tank, or the valve will get stuck.

You can find the expansion tank in the storage compartment, behind the driver’s seat, near the door on the left side under a shelf, or you can easily access it through a hatch underneath it.

In some models, the air gets fed into this compartment when filled up with compressed air.

When you draw your vacuum out of the system before servicing, this air will flow back into the system via a small bled tube that runs under the shelf above it (if filled with air).

If this air is being used for expansion and not flow, you’ll likely see bubbles or a spray of liquid when you pull your vacuum out. In this case, it’s best to fill all openings with silicone sealant and secure them before working on the system.

Many things can cause the vacuum to pump out of the system if pulled, causing the engine to run at higher RPMs (over 7k) until it cuts off (if the engine can’t cut off, the valve may not be cycling properly or stuck open).

After this, you can use engine flush to clear the system’s dirty air. If this doesn’t work, drain down the system for inspection, cleaning, and replacing all connections.


Zone valves control water flow within a plumbing system. They’re placed in the returns and let you control which zones will receive hot or cold water through the pipes that lead to them.


Hi! I I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

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