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  1. #1
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    Taco ZVC403 (blinking yellow) with Nest thermostat

    I have a Taco ZVC403 connected to 3 zone valves and boiler. I just installed a Nest thermostat to one of the zones (2, total) and the yellow status light keeps blinking at an irregular frequency. I have the R and W, 2-wire connection at the Nest thermostat.

    Is this an artifact of the Nest thermostat trying to charge off the 24vac connection?
    How do I remedy it or do I need to worry about it? When the thermostat calls, the yellow status light goes solid and everything work as it should.

  2. #2
    Join Date
    Aug 2002
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    Did it work before installing the NEST?

    Replace the NEST!

  3. #3
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    I refuse to use Nest because of all the problems I've encountered with them. I advise you to consider any other thermostat. Honeywell has proven to be reliable.
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    Questions should end with a question mark "?" Statements end with a period "."

  4. #4
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  5. #5
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    You either need a newer zone control that has a common, or you'll need to rewire your Nest correctly. Years ago, power robbing thermostats required a resistor, it's all in their instructions, which you can google and find online.
    If I do a job in 30 minutes it's because I spent 30 years learning how to do that in 30 minutes. You owe me for the years, not the minutes.

  6. #6
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    Apr 2009
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Did it work before installing the NEST?

    Replace the NEST!
    I did not have the yellow blinking prior to hooking up the Nest. I suppose I should just run a C wire and be done with it. Luckily this particular thermostat is on the 1st floor so the basement is somewhat easy to access. I'm not sure how difficult the 2nd floor thermostat will be.

  7. #7
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    Just loose that P O S!

  8. #8
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    Dec 2002
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    in a house, Appomattox, Va.
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    its still a power stealing even with the c connection. many zone controls don't work w power stealing function tstat.

    or have tech put in isolating relay, which would separate the tstat from the zone control nest
    Col 3:23


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  9. #9
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    Thread Starter
    Quote Originally Posted by billygoat22 View Post
    its still a power stealing even with the c connection. many zone controls don't work w power stealing function tstat.

    or have tech put in isolating relay, which would separate the tstat from the zone control nest
    I was thinking of adding a plug-in transformer and using the 2-wires for Rc and C connection on the tstat. This way, it would be independently powered and the power stealing "feature" would be mitigated.

  10. #10
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    Its still power steeling and unless your good at controls can damage the equipoment!

    Just replace the NEST

  11. #11
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    Apr 2009
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Its still power steeling and unless your good at controls can damage the equipoment!

    Just replace the NEST
    Honestly, I dont see how that is true with a dedicated plug-in 24v transformer? Just ordered a Elk TRG2440. I'm not trying to be a smarty pants, just trying to learn here.

  12. #12
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    Sep 2007
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    Quote Originally Posted by ChootarLaal View Post
    Honestly, I dont see how that is true with a dedicated plug-in 24v transformer? Just ordered a Elk TRG2440. I'm not trying to be a smarty pants, just trying to learn here.
    Power stealing thermostat:
    Power stealing is a way of powering a thermostat using the circuits that turn on and off your HVAC system, rather than using a dedicated power wire or a Common wire (referred to as a C-wire). ... Power stealing is designed to charge a thermostat battery which then powers the thermostat.

    We as professionals find this to be a very odd way to operate a thermostat. We have also seen many more problems with the Nest than any other thermostat. I have personally seen Nest updates cause equipment damage. So I am not a fan of them.

    So our best advice to you is to find another brand of thermostat.

    This is not to rain on your parade, so I do hope that your idea works out for you.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  13. #13
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    Apr 2009
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    Thread Starter
    Quote Originally Posted by joemach View Post
    Power stealing thermostat:
    Power stealing is a way of powering a thermostat using the circuits that turn on and off your HVAC system, rather than using a dedicated power wire or a Common wire (referred to as a C-wire). ... Power stealing is designed to charge a thermostat battery which then powers the thermostat.

    We as professionals find this to be a very odd way to operate a thermostat. We have also seen many more problems with the Nest than any other thermostat. I have personally seen Nest updates cause equipment damage. So I am not a fan of them.

    So our best advice to you is to find another brand of thermostat.

    This is not to rain on your parade, so I do hope that your idea works out for you.


    Thanks for the reply. Your advice is to avoid the issue all together instead of finding a solution or mitigate the issue.

    Since there is no dedicated power source (C-wire) and the Nest uses the 2-wire (R,W) connection to charge its battery, the appropriate solution, one would think, WOULD be to add a 24v transformer which would act as a dedicated power source for the Nest. This is an easier alternative for my particular case since running a C-wire would require more work. And would this newly added additional 2-wire connection be connected to C and Rc on the Nest?

    I am simply trying to confirm this would work. I hope someone who has done the same could chime in.

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