Updating wiring to Taco 571-2 Zone Valve--Heat No Longer Works

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Old 12-14-20, 01:24 PM
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Updating wiring to Taco 571-2 Zone Valve--Heat No Longer Works

Hello, we are doing some renovations and as part of that work we needed to move our Honeywell mercury thermostat to a new location. We used the opportunity to change the wiring from a two wire to a four wire so that we might upgrade to a smart thermostat one day.

At the boiler I reattached the wires in the exact order that they were before, with the white neutral wire coming from the thermostat in position 1, the white neutral wire coming from the boiler in position 2 and the green wire coming from the boiler in position 3. I tied in the red wire to the red wire that was coming from the boiler (picture attached).

At the thermostat I tried to copy the same that was done before, but the previous wires were not color coded. So I attached the red wire to one screw and the white wire to the other. Now when I turn on the boiler the zone valve with new wiring does not call for heat. In the zones where the wiring was not changed there is heat but it does not seem to shut off when the temperature on the thermostat was reached.

I am not sure what I did wrong here, all I was doing was trying to move over the wiring to a new position and keep it exactly the same. Any insight would be helpful.
Thanks.

Wiring at thermostat (not color coded)


Wiring at zone valve.
 

Last edited by PJmax; 12-14-20 at 01:33 PM. Reason: resized pics
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Old 12-14-20, 01:36 PM
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Welcome to the forums.

You have me confused. You ran a new four wire cable to the stat location.
We don't see that cable. We see a black and white in the picture.

Then we see a three wire cable that goes to the boiler ?
That wiring wasn't changed so why is there a question on how to reconnect it ?
 
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Old 12-14-20, 02:20 PM
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Hi Pete, thanks for your reply. Those are the before pictures and I probably should have posted the after. They are now attached. I tried to do everything exactly the same, but I'm wondering if I swapped the wiring at the thermostat? They were not color coded before, but I'm not sure if their placement matters or not.



 

Last edited by PJmax; 12-14-20 at 05:11 PM. Reason: resized pics/labeled one
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Old 12-14-20, 03:28 PM
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Your zone valve wiring starts wiht a 24V transformer. It is a series circuit.

From the transformer it goes to one side of the stat, The other wire goes from the stat to terminal #1 on the ZV. Another wire goes from terminal #2 on the ZV back to the transformer completeing that circuit so when the t-stat calls the ZV will open.

Now you need another wire that goes from #2 & #3 on the ZV to TT on the boiler. This is so when the stat calls for heat it opens and makes and end switch in the ZV which send a signal to TT on the aquastat to start the boiler so to be clear terminal #2 on the ZV needs 2 wires. One going to the transformer and one going to TT to start the boiler.

I hope this clarifies things and helps a little.

 
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Old 12-14-20, 04:44 PM
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In terms of swapping in the new cable, it looks like you did everything okay. That is assuming you didn't change anything at the other end of the brown cable (at your boiler).

A few different things come to mind:

1) everything is working fine and you aren't waiting for the delay on the end switch. I don't remember the exact time, but on a call for heat, those valves take a minute or two to open. when they fully open, they then close the end switch (completing a circuit at terminals 2 and 3) to signal the boiler there is a call for heat.

2) maybe polarity matters at the thermostat plate on your wall. The original pic has two white wires (what happened to the black wire at the ZV? one of those white wires must connect to that...) If polarity matters for that thermostat, you may have to reverse your new red and white wires on the plate.

3) your thermostat broken. at the thermostat, short your red and white wires together. wait a few minutes; does a call for heat come through?

4) you blew your transformer. As spott mentioned, there is a transformer in series with the zone valve. if you inadvertently shorted the terminals of the transformer (ie connected the red and white wires in the brown conduit) you could easily blow your transformer. Check it with a voltmeter.

voltmeter is your friend here. As for your other rooms, we will need more details about the entire set up and pictures to help sort that out.
 
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Old 12-14-20, 05:12 PM
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I labeled your picture. You do have it wired correctly. You need to check for 24vAC where indicated.
You may have shorted the wiring and popped the transformer.

There is no polarity on that thermostat.
 
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Old 12-14-20, 06:01 PM
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Hi All, thanks for your help. I walked through and double checked the wiring based on the labels and the descriptions and tightened up the connections and it did work!! Turns out it was not much to troubleshoot, but I walked away with a lot more knowledge than I started so I really appreciate everyone's help in this forum. Thanks!
 
 

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