2 Wire Boiler - Common Wire Problem


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Old 01-04-16, 08:43 PM
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Question 2 Wire Boiler - Common Wire Problem

I'm trying to setup my ECOBee3 thermostat and I need to add a common wire to my R & W thermostat setup.

Since the wire going to my thermostats is four wires and two are not used, that I would utilize one of the unused to become my common. I found 24v at the boiler and was able to use the green wire in my four wire bundle. I wired that into what I believe was the correct thermostat wire going to our bedroom.

The problem is that when I test the new common wire in my bedroom, I don't get anything. I try one lead on the common and one on either the W or R wires. When I try other thermostats in the house (four total), I get around 6v-9v when doing the same thing. This is very strange to me. I also tried moving the common to another thermostat to see if I had the wrong wire. Still same results.

I'm stumped on why I'm seeing 6v when I confirm I get 24v back at the boiler.

I've been lurking here for a while, and I appreciate any insight.
 
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Old 01-04-16, 08:51 PM
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Welcome to the forums....officially.

You need to get your C connection from the same transformer that supplies that stat.

What does the red and white wire connect to.... zone valve, aquastat ?
Pictures of your wiring can be helpful too. http://www.doityourself.com/forum/el...-pictures.html
 
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Old 01-05-16, 01:31 PM
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Here are a few pictures. Red and white connect to zones. Although I'm worried I mixed the two up when I reconnected back to tstat board.

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I grabbed the green wire to become my common (it wasn't used before)
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I'm not sure what this is
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Old 01-05-16, 02:03 PM
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is that the only transformer in the system? If so do you have a volt meter? Test between red to the stat and one terminal on the transformer which ever one you get the 24VAC between will be the common wire or where you will connect your green wire.
 
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Old 01-05-16, 02:20 PM
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Yes, I tested the spot in the first photo where I point to my new common. It tests at 24v when grounded to the casing or to the red.
 
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Old 01-05-16, 02:43 PM
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Go to the transformer and get the common from there,not from the aquastat terminals
 
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Old 01-05-16, 04:16 PM
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The thermostat does not connect to the aquastat. The thermostat connects to the zone valve and it in turn connects thru an isolated switch contact to the aquastat.

Obtaining the C from the external transformer is the correct method.
 
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Old 01-05-16, 06:39 PM
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Astuff..... there are multiple zones valves here meaning there are multiple stats. How can you connect a single stat directly to the aquastat ?
 
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Old 01-05-16, 09:24 PM
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Sorry, you are right. I had a brain fart and my mind went to an old problem non-zoned system. A sign of getting old....

Can you edit and comment out my post? The pic is not relevant but the pdf reference might be useful.

From page 11 of https://customer.honeywell.com/resou...0s/60-2278.pdf
 

Last edited by PJmax; 01-05-16 at 09:28 PM. Reason: added pdf link to post
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Old 01-06-16, 08:28 PM
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So it seems that I have the common from the right place. Why would I be getting 6v-9v on some thermostats? I can test the ecobee at the boiler, but I know I'm getting 24v there, so I wouldn't expect it to not work.
 
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Old 01-06-16, 08:40 PM
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I'm not sure what you are asking..... is your new stat currently working or not ?

In your case there you have a transformer in the aquastat and the transformer that runs the stats and the zone valves. Measuring at different points will show low and sometimes higher voltages.
 
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Old 01-07-16, 06:49 PM
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Still trying to get the common to my tstat for one zone. I find it odd that I get voltage on all common wires in all tstats even though they are not connected.
 
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Old 01-07-16, 09:13 PM
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The stats and zone valves share that same transformer.

If you follow the wiring from the transformer...... one of the wires will go to all four stats. If it was set up correctly.... the red wire from the transformer should go a splice where it connects to all the red wires from the stats.

The other transformer wire should connect to all four zone valves. That would mean that the white wire from the transformer connects to 4 yellow wires from the zones valves.

This white connection is the C connection.

Let me know if you can identify the wiring as I described it. If not... maybe you can post a few more pics of your zone valve wiring.
 
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Old 01-08-16, 05:24 AM
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What type of zone valves do you have?one set of wires are the end switches.
 
 

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