Wiring Assistance


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Old 09-24-14, 09:38 AM
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Wiring Assistance

Good Afternoon,

I purchased my house about 6 months ago and have been going through DIY'ing my way through a bunch of projects. Being in RI with Fall and Winter coming I decided to upgrade my thermostats (3 total, 2 to be upgraded).

My current setup is 3 zones - basement, 1st floor, 2nd floor. I ordered 2 Nests to upgrade the 1st and 2nd floor thermostats and am not worried about the old one in the basement. I checked both and found 2 wires run to them and will be running new 3-wire cable to each to provide a C.

Doing my prep work, documenting things ahead of time I found that both existing thermostats actually use the same cable in the basement. This leads me to believe my 1st and 2nd floors are being treated as one big zone since a heat call on one will be the same as a heat call on the other (one wire). For me I don't think this is desireable so I'm glad I'm running new cabling anyway.

This does throw in the added difficulty that now I have to rewire my Zone Valves. I think I have the correct wiring mapped out but would really appreciate your assistance.

For Reference:
Zone Valve - Taco 571-2/555-102
Aquastat - Honeywell Aquastat L8124A C
New Thermostats - Nest gen 2

 
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Old 09-24-14, 02:36 PM
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I traced some of the wiring better and found that the 1st and 2nd floor thermostats do actually have different wiring to operate independently. Here is an updated version of the image. I took the original down.

This is the current setup.


I'm running a new 3-wire wire up to the 1st and 2nd floor thermostats. Where would I ultimately connect the new common to? My aquastat does not have a C terminal. I belive I will connect it to W on the transformer to complete the circuit.

Proposed Wiring



Can someone confirm this?

Thank you,
Ian.
 
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Old 09-24-14, 03:15 PM
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R and W are reversed on the proposed wiring to the stat. It did not matter with a 2 wire stat but it does with a 3 wire stat.

Thermostat:
R = 24 vac
W = heat signal (connects to zone valve R)
C = 24 vac common
 

Last edited by Houston204; 09-24-14 at 03:41 PM.
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Old 09-24-14, 03:53 PM
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So I would go from R on the Zone Valve to W on the stat and B on the Transformer to R on the stat?
 
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Old 09-24-14, 03:56 PM
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Yes, that is correct.
Transformer B connects to stat R and stat W connects to valve R.
 
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Old 09-24-14, 05:02 PM
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Thank you.

Because I had a hard time finding it and this forum was so helpful in solving the problem here is a finished version of the wiring diagram.

Please let me know if you see any issues. I renamed some of the wiring points to more standard (from some of my reading today) terms.

Thank you,
Ian

Key Words:
Honeywell Triple Aquastat Relay L8124A C L8151A
24VAC Transformer
Taco Zone Valve 571-2 / 555-102
Smart Thermostat / Wifi Thermostat / Google Nest
2 wire to common wire conversion


 
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Old 09-24-14, 06:59 PM
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Your diagram is correct but be careful overloading the transformer. The specs on the zone valves say 21 watts each. I think three on a transformer is ok. Three on a transformer with two WiFi thermostats may be close.
 
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Old 09-24-14, 07:24 PM
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That is a good catch PJ.
A 75VA 24 volt transformer might be advisable.
 
 

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