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Endlessknight
Starting Member

9 Posts

Posted - 09/28/2017 :  10:49:44 AM  Show Profile  Reply with Quote
Greetings,

I am looking for a smart wifi thermostat that can work in a two wire, R and W, multi zone system. The sticking point is I only want to replace one thermostat, just to control that one zone, and leave the other thermostats as they are.

I've tried this in the past with the first gen Nest and one later gen Nest (2nd?) and it didn't work. The heat in the zone with the Nest would come on without the Nest calling for it, thus stay on until I tricked it into going off.

Will any of the newer Nest like the 3rd gen or Nest E work in my situation? If not is there any others that will.

Thanks in advance for any help.

stusviews
Moderator

USA
15603 Posts

Posted - 09/28/2017 :  1:37:27 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
Your heat only system has only two wires. Any programmable thermostat requires at least three wires or an external power supply. A few programmable thermostats use a battery, but not of those are controllable remotely.

If you want/need full control, then you can use virtually any remote controllable thermostat by powering it with a common 24VAC power supply.

What, specifically, are your needs?

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Endlessknight
Starting Member

9 Posts

Posted - 09/28/2017 :  3:24:46 PM  Show Profile  Reply with Quote
I've previous used a first gen nest with just two wires. Used it with little issues for four years. Then we upgraded furnaces and I started having the issues described above. At first I thought my nest was bad so I bought another and had the same issue. I just want my nest, or something similar, back.
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stusviews
Moderator

USA
15603 Posts

Posted - 09/28/2017 :  7:25:41 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
You didn't mention that the Nest originally worked. The Nest includes a battery so doesn't need an external supply.

What is your current zoned system, make, model and anything else you can provide? Also, which model thermostat did it replace? Which thermostat is in the zone that's working?

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Endlessknight
Starting Member

9 Posts

Posted - 09/28/2017 :  8:37:21 PM  Show Profile  Reply with Quote
quote:
Originally posted by stusviews

You didn't mention that the Nest originally worked. The Nest includes a battery so doesn't need an external supply.

What is your current zoned system, make, model and anything else you can provide? Also, which model thermostat did it replace? Which thermostat is in the zone that's working?



Below are pics are the current system and zone valves. The valve is question is the one label 11-15-16. That it was when it was replaced shortly after the system being installed. (Thought that might be the reason for the Nest issues, it wasn't) Also a pic of the current thermostat which was also the one used in 2012 before upgrading to nest.

Thanks for any help/input you can provide






Edited by - Endlessknight on 09/28/2017 8:41:34 PM
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stusviews
Moderator

USA
15603 Posts

Posted - 09/29/2017 :  12:54:44 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
That's a reasonably standard oil burner, but different types of valves can be used. Can you identify the valves (make, model)? The valves may have terminals labelled R and W. Do they also have a C terminal>

What specific Honeywell thermostat is the one you have (several different modes have the same appearance).

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Endlessknight
Starting Member

9 Posts

Posted - 09/29/2017 :  6:09:52 PM  Show Profile  Reply with Quote
quote:
Originally posted by stusviews

That's a reasonably standard oil burner, but different types of valves can be used. Can you identify the valves (make, model)? The valves may have terminals labelled R and W. Do they also have a C terminal>

What specific Honeywell thermostat is the one you have (several different modes have the same appearance).



The valve is a Taco zone valve model z075c2-1 and the current thermostat is a Honeywell rth5100b1009. Sorry but I don't see any terminal labels.

Thanks so much for all your help.
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BLH
Advanced Member

5600 Posts

Posted - 09/30/2017 :  03:34:34 AM  Show Profile  Reply with Quote
Page 2 of this Taco information sheet shows a typical wiring.
One of the terminals is the 'C' connection.
https://www.taco-hvac.com/uploads/FileLibrary/100-82.pdf

Do you have an extra wire in the cable from the thermostat? To be used for the 'C'? It maybe behind the mounting plate. As you present thermostat can only be powered by a battery and does not use the 'C' connection.

It depends on the way the heating contractor wired the control transformer and valves. Thermostat wired to zone valves or thermostat wired to a zone controller and it controls the zone valves.

Edited by - BLH on 09/30/2017 05:21:54 AM
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Endlessknight
Starting Member

9 Posts

Posted - 09/30/2017 :  10:40:06 AM  Show Profile  Reply with Quote
quote:
Originally posted by BLH

Page 2 of this Taco information sheet shows a typical wiring.
One of the terminals is the 'C' connection.
https://www.taco-hvac.com/uploads/FileLibrary/100-82.pdf

Do you have an extra wire in the cable from the thermostat? To be used for the 'C'? It maybe behind the mounting plate. As you present thermostat can only be powered by a battery and does not use the 'C' connection.

It depends on the way the heating contractor wired the control transformer and valves. Thermostat wired to zone valves or thermostat wired to a zone controller and it controls the zone valves.




No there is no extra wire, only R and W. When the new system was installed they retained the wiring to the thermostats from the previous system. Only two wires. My Nest worked before with just two wires. But after the change I had the issue described in the first post. Wondering if the newer Nest or something similar will work.
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BLH
Advanced Member

5600 Posts

Posted - 09/30/2017 :  1:08:02 PM  Show Profile  Reply with Quote
I saw the Green wire wrapped around the cable not connected. In your photo of the valve with a date on it.
I was hoping it was buried behind the thermostat unused.
Hope you can find an answer for your issue.
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Endlessknight
Starting Member

9 Posts

Posted - 09/30/2017 :  1:48:12 PM  Show Profile  Reply with Quote
quote:
Originally posted by BLH

I saw the Green wire wrapped around the cable not connected. In your photo of the valve with a date on it.
I was hoping it was buried behind the thermostat unused.
Hope you can find an answer for your issue.




Thanks. I'm considering purchasing a 3rd gen Nest or a Nest E and just seeing it it works. Maybe the new gens work better.
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stusviews
Moderator

USA
15603 Posts

Posted - 09/30/2017 :  5:33:32 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
It's unlikely that a newer Nest will work, but if you've got the money to play with, I wouldn't step in the way.

There's no obvious reason the original thermostat or even the Nest isn't working. What do you mean by you "tricked it into going off?"

If you connect the red and white wires together, then the heat (and fan) should turn on. When you separate them the heat should turn off. The fan may take a few minutes to turn off. Is that the result you are getting?

What happens if you install the original Honeywell thermostat using two fresh AA batteries?

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Endlessknight
Starting Member

9 Posts

Posted - 09/30/2017 :  5:47:26 PM  Show Profile  Reply with Quote
quote:
Originally posted by stusviews

It's unlikely that a newer Nest will work, but if you've got the money to play with, I wouldn't step in the way.

There's no obvious reason the original thermostat or even the Nest isn't working. What do you mean by you "tricked it into going off?"

If you connect the red and white wires together, then the heat (and fan) should turn on. When you separate them the heat should turn off. The fan may take a few minutes to turn off. Is that the result you are getting?

What happens if you install the original Honeywell thermostat using two fresh AA batteries?



Got to the bottom of my issue. Apparently it's a known design flaw in the Nest. See link below. Also it's the reason the Honeywell Wifi thermostat requires a C wire.

Long story short is the Nest calls for power to charge it's battery but the valve thinks that call for power is a call for heat, thus it opens.

Thanks for all your help stusviews. Would you happen to know of a add-a-wire kit that can go from 2 wires to 3? I've seen 4-5 to 5-6 on Amazon.com but not 2 to 3.

http://www.businessinsider.com/nest-thermostat-problem-2014-1

Edited by - Endlessknight on 09/30/2017 5:52:44 PM
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stusviews
Moderator

USA
15603 Posts

Posted - 09/30/2017 :  7:33:57 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
I happen to know that the Add-a-Wire Kit will not solve your problem.

Your choices include any standard 2-wire non-programable thermostat, any standard programmable battery powered or, with an external 24VAC power supply most WiFi and/or HA thermostats such as Insteon or Z-Wave.

Even the Nest should work with an external power supply.

A less easy solution is to install a new thermostat cable.

Edit: The link is from 2014. You may want to contact Nest for an update

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Edited by - stusviews on 09/30/2017 7:42:00 PM
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Endlessknight
Starting Member

9 Posts

Posted - 09/30/2017 :  8:08:24 PM  Show Profile  Reply with Quote
quote:
Originally posted by stusviews

I happen to know that the Add-a-Wire Kit will not solve your problem.

Your choices include any standard 2-wire non-programable thermostat, any standard programmable battery powered or, with an external 24VAC power supply most WiFi and/or HA thermostats such as Insteon or Z-Wave.

Even the Nest should work with an external power supply.

A less easy solution is to install a new thermostat cable.

Edit: The link is from 2014. You may want to contact Nest for an update



Care to recommend a external 24VAC power supply? I'm assuming I would just plug it into a wall socket and run the wire to the thermostat. Correct?

While the article is from 2014 Nest still lists this as a known issue on their site

https://nest.com/support/pro/article/Help-with-installation-and-set-up#no-power-no-common

Thanks for all your help and input. I do appreciate it.
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stusviews
Moderator

USA
15603 Posts

Posted - 09/30/2017 :  8:21:27 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
You are correct, just connect the power supply to R and C terminals. Because it's an AC power supply, polarity doesn't matter. Also, as you're powering only the thermostat and not the heating system, then virtually any 24VAC power supply will suffice.

Stu's Views is Education and Fun. What do YOU want to VIEW today?
MathLandia High school mathematics learning fun.
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Endlessknight
Starting Member

9 Posts

Posted - 09/30/2017 :  9:19:29 PM  Show Profile  Reply with Quote
quote:
Originally posted by stusviews

You are correct, just connect the power supply to R and C terminals. Because it's an AC power supply, polarity doesn't matter. Also, as you're powering only the thermostat and not the heating system, then virtually any 24VAC power supply will suffice.



So something like this: https://www.amazon.com/dp/B0010GR07O?tag=amz-mkt-chr-us-20&ascsubtag=1ba00-01000-org00-def00-other-nomod-us000-pcomp-feature-scomp-wm-4-wl-prc0&ref=bit_scomp_sav0

I notice it has two terminals. Do I only run wire from one to the common wire input on the thermostat?

Edit: Think I found what I need.

https://www.amazon.com/Venstar-ACC0436-2-Wire-24VAC-Thermostats/dp/B00755BZZC/ref=nsa_prb_sm_n_au_dka_US_pr_prb_0_0?adId=B00755BZZC&creativeASIN=B00755BZZC&linkId=4f0b06373f8304fce4a2d98f4c116792&tag=stg14-20&linkCode=w48&ref-refURL=http%3A%2F%2Fsmartthermostatguide.com%2Fc-wire-venstar-add-a-wire-adapter-review%2F&slotNum=0&imprToken=r0.lD97.tHxBYCXMsIoyRQ

Edited by - Endlessknight on 09/30/2017 10:09:48 PM
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stusviews
Moderator

USA
15603 Posts

Posted - 09/30/2017 :  10:35:10 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
No, you need to connect both wires to the thermostat, terminals R and C.

The first (and lower cost) power supply you linked to is more than adequate for your use. It'll run your entire system with room to spare--if you had a third wire. Of course, if you had a third wire, then you wouldn't need the external power supply

Edit: You may want to strip back a bit on the end of the thermostat cable at the thermostat end to ensure that there's not another wire.

Stu's Views is Education and Fun. What do YOU want to VIEW today?
MathLandia High school mathematics learning fun.
Both Stu's Views and MathLandia are free websites that do not sell anything.
Saving energy is not always free. Be a world saver.

Please don't PM with questions that can be asked in a forum

Edited by - stusviews on 09/30/2017 10:38:01 PM
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