Problems wiring new thermostat

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Old 04-04-16, 12:11 PM
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Problems wiring new thermostat

New to the forum and I'm hoping this is a problem that can be fixed.

I'm purchasing my grandparents home and want to install new programmable thermostats. Current system is hot water baseboard with 3 zones.

Before I took the existing thermostats off I went to Lowe's and grabbed 3 Honeywell 5-2 Programmable thermostats (RTHL2310b) off the shelf, because that's what I had in my current home. When I removed the old thermostat I found 3 wires (R,W,B) instead of the 2 (R,W) I found in my old home. Unsure how else to wire them I connected red wire to R, white wire to W, and Blue wire to B. Plugged in thermostat and furnace ran continuously, regardless of the programmed temp.

Most online sources tell you to go back to the furnace and check how the wires are actually connected there. Here's what I found:

Overview:
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Close up on Red White and Blue wires:
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Not exactly what I was expecting to see, but I traced them out and found the following: White is wired out to the valves that close the zones.
Red and Blue are wired to the boiler. Confirmed by crossing the bare red and blue wires. Wires touch - boiler turns on. Wires apart - boiler turns off.

The back of the old thermostat:
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No help to my amateur ability. Red was to R, white to W, and blue to B.

New thermostat:
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Through trial and error I found that red into R and white into W cause the boiler to run and run. Red into R and blue into W cause the boiler to follow program, but all zones run, when one thermostat calls. If red into R and blue into W is correct, where should white wire go, so that valves stay closed until that zone calls for heat?

I do have a multi-meter if certain readings will aid in helping me solve this problem.

Thanks
 
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Old 04-04-16, 01:00 PM
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I suspect that you have three-wire zone valves and these need a special thermostat that energizes one wire to open the valve and then energizes the second wire (both energized from the third wire) to close the valve. Post the manufacturer and model number of the zone valves as well as a couple of pictures and someone should be able to verify.

If this is true then you could either install an intervening relay to give you the three-wire control or go to a much more expensive commercial thermostat that will control the valves directly. You won't find a compatible thermostat at the big box mega-mart homecenter.
 
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Old 04-04-16, 01:36 PM
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Welcome to the forums.

Be careful doing anything yet. If you need heat right now..... leave the old stats in temporarily.

I see some interesting wiring and I see a bridge rectifier inside that box which would change AC to DC. From your description I believe a regular battery operated stat will work.

Three wires to the old stats was not normal but was an upgrade in wiring. The B terminal is used for heat anticipation at the thermostat. Cap it off. It's not needed. You only need to connect the red wire to R and the white wire to W/AUX.

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Old 04-04-16, 01:58 PM
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From your description I believe a regular battery operated stat will work.
Not if he has three-wire zone valves.


Three wires to the old stats was not normal but was an upgrade in wiring.
I disagree, three-wire zone valves were once VERY common.


The B terminal is used for heat anticipation at the thermostat.
Sometimes, but thermostats that used the three-wire configuration for heat anticipation are not just old now but absolutely ancient.

Bottom line, until sarm returns with the requested information on the zone valves no one can give an absolute answer to his problem.
 
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Old 04-04-16, 03:13 PM
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The model number off the old stat would be helpful too.
 
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Old 04-04-16, 07:51 PM
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I have seen the old T87 round Honeywell thermostats wired to control power open / power closed valves this way.

The Honeywell TH8110U will support this Series 20 operation.



I work with power open / power closed valves but I always install relays since I have boiler water and chill water.
 
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Old 04-04-16, 09:57 PM
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The only problem is he doesn't have a T-87 and his stat has a B on it and the T-87 uses the Y.

We still need some missing information.
 
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Old 04-04-16, 10:52 PM
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It is a SPDT thermostat.

It looks like a Robertshaw 400 series.

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Old 04-05-16, 09:53 AM
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Ok. This activity is awesome. I don't live at the house currently, so I had to run over to take the pics this morning. I took a lot. Hopefully I covered the questions from overnight, plus anything that may arise.

Type of valve:
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Type of old thermostat:
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Overviews
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Old 04-05-16, 11:28 AM
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Thank you for the pictures. This is the important one.

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AUTOMAG - Technical Information


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So now we know for sure what we're working with..... now comes the fun part.
 
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Old 04-06-16, 06:33 AM
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Ok, thanks for the schematics. Help me understand what I'm looking at.

Clearly there's the addition of a "CNV Relay". Is this something I can just buy off the shelf or from Amazon? Is it called anything other than CNV Relay? All 3 wires go into the relay and 2 come out. I'm guessing the one that goes directly to the thermostat is red, then the white goes back to the power supply, and out to the thermostat? I feel like I'm missing something here.

Reading the attached link, am I seeing that a CNV Relay is needed for each valve, is that correct?

There also appears to be the addition of something on top of the Automag Power Supply. Or is that just not pictured in the first schematic? The top of the power supply is cut off in the first schematic.

Now there's 3 thermostats at play here. How does that figure into the 2nd schematic? There are wires coming off the white from relay to power supply and power supply to thermostat that say "additional zones".

I can build a deck, or a whole addition, put up drywall, siding and roofing. Change a faucet or a ceiling fan. Electrical stuff still throws me from time to time. Sorry for the excessive questions, but I really appreciate the help.
 
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Old 04-06-16, 07:05 AM
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That relay is just a single pole double throw (SPDT) relay with a 24 VAC coil.

I always use the bigger stronger DPDT relay because I have had to go back and replace the smaller quieter relays after 2 years many times.

The DPDT relay is numbered differently since Common is 1, N.C. is 2 and N.O. is 3 but it would be my choice.

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Assisting you with the rewire from the internet would be the tricky part.
 

Last edited by Houston204; 04-06-16 at 07:32 AM.
  #13  
Old 04-06-16, 08:03 AM
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If you are willing to spend more time and money.... With three zones it might be cleaner in the end to get the zone controller. AZC 4060-P in the referenced link AUTOMAG - Technical Information
 
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Old 04-06-16, 08:41 AM
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I guess at this point I'm looking for the most cost effective solution.

I've got $80 invested in the 3 thermostats hanging on the walls.

Do I:
A) Buy 1 or several devices to install near the boiler to "make" the thermostats I have work with the system as it sits. As PJMax and Houston 204 suggest.

B) Update the wiring and devices to work with the thermostats that are installed. As Astuff suggests.

C) Scrap those thermostats and purchase another model that can wire directly to my 3 wire system. I'm assuming there has to be another model that is plug and play. I mean I'm not on some exotic system, right?
 
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Old 04-06-16, 09:19 AM
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I would consider the TH8110R thermostat.
 
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Old 04-06-16, 10:58 AM
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Amazon has TH8110R at $104. I'm sure I could shop around, but for now let's go with that price. AutoMagzonevalve.net lists an AZ40 at $250. Same site has the CNV84 at $27.50 a piece.

So following my number logic from above:
A) Buy 3 CNV84 from AutoMagZoneValve.net for $82.50, and likely spend some time figuring out the wiring.

B) Buy 1 AZ40 for $250, spend more time figuring out wiring, and end up cleaning up my existing wiring.

C) Buy 3 TH8110R for $312. While this is the plug n play option, it is clearly the most expensive, but in addition to spending $312, I'd be scrapping $80 worth of thermostats.

Does that summarize it all or am I missing something else? It seems like option A is the most reasonable, assuming I can figure out the wiring. I don't have a relative in the HVAC field, but I do know a pretty handy electrician.
 
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Old 04-06-16, 11:22 AM
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3 DPDT relays for $6.26 each is the cheapest option.

You would also need some squeeze on connectors, some wire, & some screws to mount the relays.
 
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Old 04-06-16, 11:40 AM
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Well that certainly is the cheapest option. Thanks for the Amazon link!

Now to be perfectly honest that thing looks more than a little intimidating.

I'm looking back over the photos I took of my system and I'm trying to visualize where that goes. If I order from Amazon, is it packaged with any kind of schematic? Or is one of the previously shared schematics going to be the best I'm going to find?
 
 

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