Troubleshooting Hot Water Zone Valves

January 26, 2001
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In zone valve setups, a separate zone valve is installed in the pipe to or from each zone. In most installations, the zone valves are in the returns, where the water is cooler. The cooler temperatures are easier on the valves.

It has been the practice of some to place them in the supply using a manifold just above the boiler; this is often in conjunction with the “pumping away” concept.

Each zone valve is controlled by its own zone thermostat. End switches in each zone valve control the central circulator and the burner.

On a call for heat, the valve is opened. When it reaches the fully open position, the end switch “makes” (makes contact), causing the aquastat relay to pull in, starting the circulator and the burner. If the circulator control and high limit switches are closed, the circulator and burner come on.

All of the end switches in a system are wired in parallel. This ensures that the circulator and burner are powered when any zone calls for heat. The circulator and burner shut down when all the thermostats are satisfied.

There are some preliminary things we should cover before looking at a specific zone valve.

Note: The following troubleshooting procedures are intended to familiarize you with some basic types of systems. For detailed instructions on particular zone valves, refer to the manufacturer’s spec sheets.



Troubleshooting Tips

  • If there is no power to the powerhead, it will be the service-person’s responsibility to find the trouble, as the problem is not in the zone valve.
  • If the valve is sticking, remove the powerhead (if it is the type that can be removed) and operate the powerhead electrically while holding it in your hand to see if the motor assembly operates freely.
  • Also, try to move the valve stem assembly by hand to be sure that the paddle is free. Some exceptions will be where a plunger will have to be pushed down manually to see if it is free, as these types of valves do not employ the paddle-type valve system.

  • If the motor assembly is sticking, change the powerhead. If the plunger or paddle is sticking, a plumber will have to change the valve assembly.
  • If the zone valve problem is found at night and it can wait until the next working day, or you do not have the parts with you, open the valve manually.
  • Get all the information, including valve name, model, serial numbers, and pipe size. On multiple installations, you must state which valve failed and tag it.
  • If the powerhead is unavailable or outdated, it will need to be replaced.
  • Zone valve servicing can be made simple when you realize that they are broken down into three-wire, four-wire (Dole), five-wire, or six-wire (old Series 20) models. The exceptions to this include valves that identify wiring by labeling terminals “thermostat,” “transformer,” and “end switch.”
  • It is possible to put most zone valves on manual to ensure that there is heat until the powerhead or valve can be replaced.
  • At times, it will be necessary to make a replacement by using a changeover valve or powerhead.


  • Zone Valves

    Zone valve systems use a thermostat and zone valve for each zone, and one central circulator.

    For these systems, the preferred valve is a two-position (open or closed) straight-through valve, such as the Honeywell V8043. These valves are standard for residential applications.

    The exploded view of a typical Honeywell straight-through type zone valve (Figure 1) shows how it is designed and constructed. Its main components are:

  • Low-voltage motor;
  • Auxiliary (end) switch;
  • Valve housing and seat; and
  • Valve stem and ball.
  • On a call for heat, the low-voltage thermostat makes, powering the valve. The motor drives and swings the ball off the valve seat. Just before fully opening, the end switch makes, signaling the aqua-stat relay to turn on the burner and central circulator. When the thermostat is satisfied, power to the motor is cut off and the return spring closes the valve by swinging the ball back onto the valve seat (Figure 2).

    All the end switches in a system are wired in parallel so that a call for heat from any zone powers the burner and circulator. Diverting valves operate the same way, except that the ball closes the alternate port when the valve opens.

    For proper operation, it is important to install the zone valve so that the water or steam flows in the direction of the arrow on the valve body (Figure 3).

    The compact design allows these valves to fit under the covers of most baseboards. The complete powerhead can be replaced without disturbing the valve body, and does not require breaking line connections or draining the system.

    The rubber plug is rotated by water movement and the closing action against the seat. The rotation seats the ball on a different spot during each cycle, ensuring long part life. The rotating action also cleans the valve seat as it closes. The stainless steel stem resists corrosion, and the three O-rings ensure a leakproof seal.

    Models are available with sweat or flare connections, and for normally open or normally closed operation. A reverse-acting thermostat is required to control normally open valves.

    If power to the valve fails, it can be opened manually, allowing some circulation by gravity (Figure 4). The valve automatically returns to normal operation when power is restored. The manual-open position is recommended during soldering to keep from overheating the ball plug. Normally open valves, which are normally open when de-energized, have no manual opener.

    Manual valve operation is a real convenience in new construction. The usual construction sequence is to install thermostats after drywall work is complete, yet drywall installation often requires heat for drying. The manual option allows the hydronic system to provide heat even without thermostatic control.

    Honeywell zone valves are low-voltage, straight-through or diverting types, or high-voltage, straight-through or diverting. Each valve is controlled by its own thermostat. The V8043 provides low-voltage, straight-through control of hot water, and the V8044 provides low-voltage diverting control for bypass hookups.

    Low-voltage power for all the valves in a system is supplied from a single source, either an external transformer or the internal transformer of the aquastat relay. The transformers in some models of the L8124 and L8148 are sized to power two or three zone valves directly. Figure 5 shows typical wiring for the V8043E and V8044E models, and Figure 6 for the V8043F.



    Troubleshooting These Valves

    1. Check for 24 V at TR terminals.

    2. With the thermostat calling, you should not read 24 V at TH terminals. If you do, the thermostat is open.

    (Note: This depends on whether the wiring from the thermostat is direct to TH, or if the wiring is through the transformer and wired to TH and TR.)

    3. When power is applied, the motor should open the zone valve. If power is applied to the zone valve and it does not open, replace the motor or the head.

    4. If the zone opens but the relay does not pull in, jump out the end switch on the zone valve. If the relay pulls in, replace the end switch or the head.

    5. If the relay does not pull in, the problem is in the relay or the wire to the relay.

    If you suspect a service problem is caused by a faulty valve, follow these procedures to check its operation:

    1. Raise the setpoint of the zone thermostat above room temperature to call for heat.

    2. Observe all control devices. The valve should open, and the end switch should close the circuit to the circulator or other valve at the end of the opening stroke.

    3. Lower the setpoint of the zone thermostat below room temperature so that it satisfies.

    4. Observe the control devices; the valve should close. The auxiliary equipment should stop unless the end switches are wired in parallel and another zone is calling for heat.

    If the auxiliary equipment continues to run when the zone valve satisfies, lower the setpoints below room temperature on all the zones and repeat the procedure.



    Valve Repair

    If the valve is leaking, drain the system and check the O-ring on top of the valve body. If it is the source of the leak, replace it to restore a tight seal.

    If the gear train is damaged, replace the powerhead assembly. If the valve has a new-style (Series 6) body, it does not require draining the system or breaking line connections. If the valve has an old-style body, the valve body must be converted to accept the new powerhead with a conversion kit, which does require draining the system.

    McElwain, president of Gas Appliance Service Training and Consulting, teaches service and troubleshooting skills. The company has troubleshooting guides covering 38 topics, and teaches a seminar series on the Fundamentals of Gas, Circuitry and Troubleshooting, Hydronic Controls, Electric Ignition Systems, Advanced Electric Ignition Systems, Powerpile Systems, and Conversion Burners. Contact McElwain at Gas Appliance Service Training and Consulting, 22 Griffith Dr., Riverside, RI 02915; 401-437-0557.

    Publication date: 01/29/2001

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