The Amtrol expansion tank on my boiler needs to be replaced but the installers did not include an isolation ball valve. I can close the returns, but the water will still drain down from the upper floors of the house unless I can close the zone valves. The zone valves can be put in the "always open" position by pushing the latch towards the pipe, but is there a way to put the zone valves into a forced-closed position? If the system electrical is turned off when the thermostat is not calling for heat, will the valves be, and remain, in the closed state?

P.S. Here are pics of one that was replaced with a new one. It is not really designed to be user-serviceable. The outer shell is riveted in place. I do not see a hefty spring.enter image description here

Taco Zone Valve



is there a way to put the zone valves into a forced-closed position?

Taco zone-valve (wax piston actator):

  • disconnect top wire at contact marked #1 and wait 2 mins, or
  • disconnect all wires, wait two minutes, rotate head and remove.

Zone valves with a synchronous motor

  • remove the head.

Further to Tkw's answer, heres the inside of a zone valve. Note the two springs that close the valve when the motor is not powered.

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With some zone valves, where the manual-opening lever is located you can peek in and see the toothed segment that is moved by the motor's gear (which typically turns at only 3.5 rpm)

What you show in your updated question looks like a Taco zone-valve

enter image description here

The bottom cast-metal part is the actual valve.

The top part, in a plastic enclosure, is just the Zone-Valve Power-Head. This is a separately purchased part and is designed to be replaced without disturbing the plumbing.

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Once the power head is separated from the bronze valve body, the valve will be shut and there is no way for any of your heating controls to open the valve.

If you look at the cutaway diagram in the manufacturers brochure you'll see there is a very strong spring in the base.

enter image description here

That spring holds the valve closed when the power-head is disconnected.

If you want to be 100% sure the valve remains closed regardless of what your controls are doing, just pull the power-head off.

Procedure to remove power unit and replace with Taco 555-050RP, 555-151RP, 555-154RP or 555-173RP (as applicable) replacement power unit:
1. Turn off room thermostat.
2. Mark wires; 1, 2, and 3, according to terminal strip numbers on power unit.
3. Disconnect wires from power unit terminal strip. Do not allow wires to come in contact with each other or other objects.
4. Wait two (2) minutes for power unit to cool down.
5. Push down slightly, and rotate power unit clockwise (as shown) to remove, and lift off.
6. Position new Taco replacement power unit on valve body, push down slightly and twist counter-clockwise to assemble onto valve body.
7. Reconnect wires marked 1, 2, and 3 to their respective terminals on the replace-ment power unit.
8. Check to make sure that the manual operation lever is in the auto position before returning the thermostat to normal operation. (Note: no manual lever on 555-173RP.)

Though just disconnecting the wiring (or just wire #1) ought to be enough.

  • And all zone valves work on the same principle? Absent a call for heat (for whatever reason, including no power) the spring closes the valve, effectively isolating the zone?
    – TRomano
    Nov 20 '16 at 21:26
  • @TRomano. I don't have experience of all zone valves on the planet but this is a Siemens zone valve and I'm pretty certain that Honeywell zone valves will work the same way - with return springs. It is usually pretty easy to remove the top of a zone valve without disturbing the plumbing. You are meant to be able to replace the motor in situ without disturbing the valve. In this case, a couple of plastic latches hold the top on. You might like to open yours up and have a look. Nov 20 '16 at 21:28
  • @Tromano, see updated disassembly photos. Nov 20 '16 at 21:36
  • Yours looks very different from mine. Mine cannot be taken apart to be serviced. I will post a pic.
    – TRomano
    Nov 20 '16 at 21:38
  • 1
    What a great & thorough answer. Mar 19 '18 at 23:54

That's the way zone valves work. When the thermostat is not calling for heat, they're closed. Otherwise you would have heat going all the time the circulator runs in all zones.

  • 1
    I just took a zone-valve apart this afternoon! there were two pretty-strong return-springs that closed the valve when there was no power to the synchron-motor. Nov 20 '16 at 20:59
  • I just wanted to make sure that "thermostat not calling for heat" and "no electrical power" are the same state, as far as the zone valve is concerned.
    – TRomano
    Nov 20 '16 at 21:24
  • @Tromano, In UK plumbing (e.g. Honeywell S-Plan) the thermostat contains a switch that directly provides power to the motor in the zone valve when closed. If the thermostat is not calling for heat there can be no power at the valve motor. Low voltage systems (as used in the US) presumably have a solenoid in the controller but won't power a zone valve if the thermostat is not calling for heat. Nov 20 '16 at 21:40

You did not shown a picture of the existing expansion tank or say it needs replaced. There are many ways to install a shut off valve in a copper line that has water in it. Sometimes you get wet doing it and sometimes you don't. Also the type of tank dictates the type of fix required.

  • The first sentence of my question states that it needs to be replaced. The tank (4 gallon Amtrol) isn't connected by copper but by a black iron nipple threaded into the bottom port of the air separator. I don't mind getting wet. I would like to avoid draining the hydronic system.
    – TRomano
    Nov 26 '16 at 14:07

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