Another thermostat wiring question


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Old 06-04-14, 04:10 AM
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Another thermostat wiring question

OK, here's the situation:

I have a gas boiler that powers my hot water baseboard heat and a separate AC unit, each controlled by separate thermostats. I want to combine them into one thermostat (a Venstar t5800). The stat for the boiler only has two wires, while the stat for the AC is battery powered.

My question is: Where do the wires need to go in the new thermostat, and am I going to have to run more wire so I can power the Venstar?

This is the stat for the AC


This is the one for the boiler


And a shot of the wires for the boiler stat
 
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Old 06-04-14, 08:53 AM
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Welcome to the forums.

The Venstar may not work for you. You require a thermostat that can split the heat and A/C units. That would mean the thermostat would have a separate Rc and Rh. You could use that
thermostat with a separate relay to control the heat.

I see extra wires at the thermostat which is a good thing. Is your A/C unit a standard air conditioner with no heat ? Your current thermostat has a heat (W) wire connected.

You could go to the air handler and confirm what terminals the wires are connected to and post them here.
 
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Old 06-04-14, 09:54 AM
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As far as I know, the AC is just a cooling-only unit. I've just purchased the house (it was a foreclosure), so I don't know as much about the systems as I'd like to yet. I'll try to get into the attic today and get a pic of the wire connections.

On the off chance I can't use the Venstar, is there another thermostat (preferably one I can control via smartphone) that you'd recommend for the way things are set up already?
 
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Old 06-04-14, 09:58 AM
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I'm sure there is something in the Honeywell line that will be perfect for you.

Just to be clear.... the Venstar would work it would just require a relay for the heat.

The forum pro, Houston, will stop by and make a thermostat recommendation for you.
 
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Old 06-04-14, 11:23 AM
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Oh, I see. So, basically I would just need to run some more wire? If so, I'm not adverse to doing that, since I'd have to relocate the wires for the boiler stat to the wall where I want the new stat to go anyway.
 
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Old 06-04-14, 01:42 PM
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Honeywell RTH 6580 is a nice Wifi Tstat and I think it would fine for your application.
Geo
 
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Old 06-05-14, 04:08 AM
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Not sure if this is what you need, but I couldn't find an access panel on the AC unit that would let me see where the wires terminated. Looks like I might have to remove some bolts to take the panel where the wires come out, off. Does that sound right?



Didn't know if this info would help:
 
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Old 06-05-14, 06:16 AM
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From the air handler to the Tstat you need ,
Red. To RC
Blue. To C
Yellow To Y1
Green To G

From the boiler

Red. To R or RH. BE SURE TO REMOVE JUMPER BETWEEN RC /RH
White To W

If you have a meter check between Blue and Red at the air handler to be sure you have 24volts but I am fairly sure you will.

Geo
 
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Old 06-05-14, 07:50 AM
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So just to be sure I have everything right in my head...

The blue wire in this pic



is my power from the handler to the stat, but since the stat is battery powered, it was not connected. So all I need to do is wire it in to the new stat and I should be good to go for power. Is that about right?
 
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Old 06-05-14, 09:26 AM
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What are you using for the new stat ? The Venstar doesn't have an RC - Rh jumper unless I missed it.
 
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Old 06-05-14, 09:28 AM
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If this Stat is strictly for your AC then yes,remove the white wire as it is not needed from the air handler and it looks like it is disconnected there anyway,and put that red wire on the RC terminal.
Now pull a new 2 wire from the boiler and put the red on RH and the white on W or W1.
Geo
 
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Old 06-05-14, 10:15 AM
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That's the old stat for the AC. I haven't changed anything yet, I wanted to make sure I had a good idea what I was doing before I started rewiring things.

Geo: Thanks for the info, I'll test the blue wire for 24 volts and see if I can get things wired up in the next day or two
 
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Old 06-05-14, 01:36 PM
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Ok, got up in the attic to start testing things and getting it all prepped for rewiring and I think I've hit a snag. My earlier pic of the wires coming out of the air handler were misleading because of all the shadows. I tried to take a better one here:



So if you look at the previous pics of the wiring of my current thermostat and this pic, then it looks like the red wire is connected to the red going into the air handler, green to green, but the blue and white(ish) wires aren't connected to anything (not sure why the white is connected at the thermostat end, but not at the other end).

The yellow wire is connected to the line that runs outside to the AC unit, as well as the blue wire coming out of the handler being connected to the same line.

Then while I was messing around up there, losing my bodyweight in sweat, I found this:



Not sure if this helps at all, but I thought it might save me from having to take more bad pictures.

So my question now becomes, where do I get power for the faceplate of the new stat? I tried checking all the lines coming off the air handler but I couldn't get any readings (that doesn't mean there isn't power there, it's just the first time I've ever used a multimeter and I'm not 100% sure I did it right).

This also got me thinking that if it was going to be difficult to get power from the air handler, maybe I could get it from the boiler instead, so:





I noticed that there was an unused connection "C" on the boiler. I didn't know if that the same as the "C" connection on the Venstar stat that I'd need for powering the faceplate.

And lastly, here's the connections on the Venstar:

 
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Old 06-05-14, 03:12 PM
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Between the blue wire going to the condenser (outside unit) and the red wire at the air handler you should have 24 volts AC ,in which case tie the blue wire that is loose to that blue /white connection and walk away,make the connection at the Tstat as I described before.
If you are not in a rush check on Ebay for the Honeywell RTH6580 much cheaper, I have bought 2 on there and haven't had any problems,you can always download full instructions on line

Geo
 
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Old 06-06-14, 04:04 AM
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Ok, I think I finally understand how to get power to the stat. Looking at the Venstar I didn't see an RC terminal. Which terminal on the Venstar do we need to wire the red wire from the air handler to?
 
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Old 06-06-14, 04:48 AM
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What is the model is the Venstar?
 
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Old 06-06-14, 05:09 AM
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I just checked online and if it is a T5800 or T5900 the red wire will go on R and if you plan to use it for the boiler you will need to install a relay as PJmax has stated that would be switched from C and W1 on the thermostat,best bet now is to get the cooling working first then we can tackle the heat.
Geo
 
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Old 06-06-14, 05:21 AM
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Gotcha. I'll try to get the AC all hooked up tonight and let you know how it works
 
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Old 06-06-14, 10:17 AM
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It sounds like you have the A/C and power part of the thermostat taken care of.


You have a spare wire in your thermostat cable. Connect the white wire to W1 and put a wire nut on it at the air handler end. You'll need to get your two wires from the boiler to the air handler location. I see the air handler is in the attic so it may be easier to just get two wires from the thermostat location to the boiler.

If you want to run the two wires now..... one gets connected to C and the other wire gets connected to W1. DON'T connect them at the boiler yet.
 
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Old 06-06-14, 02:20 PM
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Got it all wired up for ac, plugged in the faceplate and everything works great.

You're right, it would be a lot easier to run wire from the thermostat to the boiler rather than all the way from the basement to the attic. Doing it that way, you're saying I need a new wire connected at the thermostat at w1 and c, and then down into the basement. Once I've got the wires down there, what comes next?
 
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Old 06-06-14, 02:31 PM
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You would connect the two wires from the thermostat to the coil of a 24vac relay.
Then the two wires from your boiler would connect to an open set of contacts.

Here is a usable relay. There are 24vac relays like this all over the internet. The type is not important as long as it has a 24vac coil.

Amazon/Supco-General-Purpose-Current-Contacts/
 
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Old 06-07-14, 04:36 AM
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Another relay choice would be a RIB https://estore.industrialcontrolsonl...01B%5B1%5D.pdf
You could mount it on top of the controller where the thermostats wire go now, cut and cap the spare wires connect W1 to white/blue and C to white/yellow and yellow to T and orange to T on the controller where the old thermostat wires were removed.
Geo
 
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Old 06-07-14, 04:50 AM
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One other thought would be if there is room on top of the controller would be to mount a 4"square using a close nipple,put the RIB on that and bring the new thermostat wires into it and make all the connections in there bring the Yellow and Orange directly to the TT terminals that way you would not have so many wires in the controller which would be more advisable.
Geo
 
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Old 07-29-14, 06:42 PM
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Finally got around to wiring up the boiler to the thermostat using the Supco relay like pjmax suggested. I'm running into some problems, and I'm not sure exactly where to start looking to fix it.

Here's what I did:
Pulled new wire from the stat to the relay. The white wire went to w1 and the red went to c on the Stat, then red to #3 terminal on relay and white to #1.

From the relay, I took red wire from #4 terminal to r/t on the boiler and white from #2 to g/t on the boiler.

The problem came when I tried to fire up the baseboards to test. The circulator pump on the boiler kicks on when I switch to heat, but no hot water circulates to the baseboards. The pipe directly connected to the circulator pump is hot, but gets noticeably cooler further away from the pump.

The only other thing of note that happens when I switch the Stat over to heat is that it says "heating (2nd stage)". I was under the impression that connecting the boiler to the w1 on the Stat would make it use 1st stage heating.

Thanks in advance for the help
 
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Old 07-29-14, 10:54 PM
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When you switch over to heat..... does the relay close like it should ?

Pump is running but no circulation..... possibly a zone valve not opening... if used.
 
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Old 07-30-14, 11:16 AM
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I assume the relay is working correctly, though I'm not sure. Would the pump even kick on if the relay was wired wrong?

I think I have just the one zone for the baseboards
 
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Old 08-18-14, 04:23 PM
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After fiddling around with the relay and the boiler I think I may have burned out the relay. Nothing happens now when I switch on the heat.

I'm going to try the RIB relay as geo mentioned. I know you said that the yellow and orange wires from the relay go to the T terminals on the boiler, but does it matter which one goes to r/t and and which one to g/t?
 
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Old 08-18-14, 09:39 PM
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It's pretty hard to burn the relay out unless you connected 120v to the coil.

You have two wires coming from your thermostat. One is Common and one is 24vac in heat mode. You have two wires going to your existing heating equipment. The wiring is extremely basic. Your dealing with AC voltages...there is no polarity.

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