Install WiFi Thermostats with Aquastat relay and 3-taco zones


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Old 09-17-22, 08:32 AM
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Install WiFi Thermostats with Aquastat relay and 3-taco zones

This looks like a common question that has been answered, but couldn't find anything to specific to my exact setup. Apologies if this has been addressed in another thread and I just didn't understand.

I'm looking to replace 3 programmable thermostats with WiFi thermostats (Nest or Ecobee). They currently use two wires on W/R and a bridge from R->RC. I have an Aquastat L8148J relay and three Taco 571-2 zone valves. I just have a boiler that provides heating, and a separate mini-split system for cooling on it's own dedicated wireless thermostat. One day I'd like to figure out if I can wire up the cooling somehow as well to one of the new thermostats, but for now just want to figure out the heating-only to start.

I'm not sure how to rewire this for my application. The current connections I don't quite understand. See photos and diagram below of current connections.


I had read the new common wire should go to W/Z - but the existing white (W) from the current thermostats currently go to Z (with bridge to W/TP) which confused me.

How should I go about rewiring this to add the smart thermostats? One of the thermostat wires is an 18/5 and only using the R/W wires. I'll be running new 18/5 wires for the other two today.

Thanks in advance for walking me through this.
 
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Old 09-17-22, 09:16 AM
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The wiring diagram is not what you have.... it's what you want to do.... correct ?

Typically zone valves are not run directly off an aquastat.
Three zone valves should never be run form an aquastat.
You should have a separate 24vac transformer for the zone valves.
You thermostats should be connecting at the zone valves.

Post some pictures of your valves and the wiring.
 
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Old 09-17-22, 10:38 AM
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This wiring diagram is what I have. I'm not sure how to support a WiFi thermostat from this configuration. Sounds like it might not be right which is concerning. All the heating works fine...or seems to. I haven't touched this since I bought the house.





 

Last edited by PJmax; 09-18-22 at 12:06 AM. Reason: resized/labeled pic
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Old 09-17-22, 10:55 AM
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There is a transformer inside the aquastat. Three zone valves require 40va of 24v power to operate. I didn't think those transformers were 40va. I thought they were 20va - 30va. I'm checking further.

I would not recommend adding three wifi stats on that aquastat.
A 24v transformer is around $35. A replacement aquastat is over $200.

It would not be hard to add a transformer. I'd give you a diagram.
 
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Old 09-17-22, 11:20 AM
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That would be great thank you.

Are the 24v transformers for that brand fairly universal or do I need a specific model?
 
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Old 09-17-22, 12:19 PM
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Honeywell AT72D is widely available. It's 24vac @ 40va. Some home improvement stores carry it.
The TR75 is a 24vac @ 75va with circuit breaker. Not necessary but a pro choice.
Shop around.... the prices are all over the place.
Both can mount directly on your service switch box.

AT72-D
TR75VA005 best choice

Based on the systems temps.... you shouldn't run three valves. Chart shows two max at 77
Resideo L8148 operating specs -pdf
 
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Old 09-17-22, 03:58 PM
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Just ordered the TR75. 3 days out.

Based on the systems temps.... you shouldn't run three valves. Chart shows two max at 77
Just want to confirm that by this you mean I should not run three valves off the Aquastat as it is today, but if I add a secondary transformer and run them off that instead they should operate fine, including if I add smart thermostats. Is that right?

I think I get this conceptually after reading it in more detail now that I'm home, but still wouldn't have a clue how to wire it. That diagram would be a life saver next time you get a chance. Much appreciated for all the help. I never would've caught that transformer issue...nor has any other HVAC guy who's looked at my system.
 

Last edited by PJmax; 09-18-22 at 12:08 AM. Reason: removed un-needed pics
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Old 09-18-22, 12:15 AM
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That's an older aquastat with a real robustly built transformer.
The newer replacements don't use the same high quality transformer.
With three zone valves that transformer had to be running hot.

Didn't need your last pictures.
The wiring is very easy and can be a lot neater than it had been.

You mentioned possibly adding in A/C to one of the stats. If the A/C stat and the heat stat were next to each other you would have two cables to connect to the new stat. If both cables aren't there you'll need to run a cable with more wires for the future A/C expansion. You could add the A/C in at any time but keep in mind the boiler wiring will change for that thermostat as the C must come from the A/C when using two systems.

I'll post a diagram later today.
 
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Old 09-18-22, 12:30 AM
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Actually.... you've got pretty good knowledge of your system. Here's the basic diagram.
You have five wire cables going to the zone valves. The colors aren't really correct.
Rewire them so that you have white on 1, blue on 2, green on 3.
Red signifies 24vac
Blue signifies C (common)
Blue and red are connected to the transformer but there is no polarity regardless of transformer markings.


The blue and green wires as shown going to TT will connect to T and Tv as shown in picture 1.
There will no longer be a wire on Z.

 
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Old 09-18-22, 08:56 AM
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Perfect. Makes sense.

Last question for now: for installing the TR75...my service switch box has a direct line/common to the Aquastat. Guessing I want to splice it between those points and have one pair going to each the Aquastat and the new transformer. Is that right?
 
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Old 09-18-22, 09:11 AM
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Yes.... you want both to be powered to work with the switch.
 
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Old 09-19-22, 05:26 AM
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In your diagram there is an intersection of the common blue wires from the thermostats & the blue wires from the zone valves. That is a connection at that point and not a jump on the diagram right?
 
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Old 09-19-22, 07:10 PM
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That is a connection point.
Not necessarily in that exact location but all three # 2's all three C's are connected together.
Everything in blue is C.
 
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Old 09-22-22, 05:00 AM
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It works! You're the man!

In order to get the new wiring for my second floor thermostat I need to run it through the attic and then down two floors to the basement. My A/C air handler is up there in the attic so I'm going to run an extra wire for that too for future expansion. Right now it just uses a wireless thermostat which is right next to the heat thermostat on the second floor.

Just going back to your previous comment about the C-wire change if I consolidate these together...I'd need to have the C wire from the boiler go direct to the A/C air handler, and then a C-wire from the air handler down to the thermostat to power it?

 
 

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