Weil-McLain meets Taco

Old 10-05-19, 03:15 PM
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Weil-McLain meets Taco

Good afternoon,

I am confused and need help. I have a Weil McLain CGM-5-PI that was a single zone system. I am trying to make it a two zone system using the Taco 2 way zone valve. I am having a hard time figuring out the wiring. Every diagram shows the #2 and #3 post on the Taco valve go to the TT post on the boiler.

My Weil McLain has a built in transformer. There are two wires that currently run from inside the boiler to my thermostat. From my understanding, a wire runs from the transformer to the #2 post and than to one of the TT post on the boiler. If I were to use the posts that run to my thermostat now, does that mean itís going back into the transformer again? I am missing something...
Old 10-05-19, 03:25 PM
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To elaborate

current system

terminal G on boiler/transformer is the white wire going to the thermostat

terminal R is the red wire going to the thermostat

Old 10-05-19, 04:17 PM
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The manual states that you run a second transformer for the valves and that #2 and #3 run to the TT terminals. I guess I donít understand if the R and G terminals are the TT terminals. If there is a built in transformer, Iím afraid that connecting to those terminals makes the power go through the boilers transformer?
Old 10-06-19, 05:21 AM
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Your boilerís factory controls provide for only one zone.

If you are unfamiliar with relay control wiring, youíll need to purchase and install a zone control panel like this:

If you wish to DIY it, you could always assemble your own control panel...like this:
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Old 10-06-19, 08:03 AM
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Part of the confusion here comes from two systems with different wire labels.

Units with TT terminals are activated when they are connected together. In a sense, TT is a dumb system designed to be independent of other systems.

Modern thermostats with 12 or more terminals activate many things burners, fans, AC and whatever.

Thermostat electronics are powered by one side of 24 VAC transformer connected to terminal ďCĒ for common. One side of relay coils on other units in system is also "commoned" & connected to C.

For heating oher transformer terminal is typically connect to RH. When there is call for heat connects RH to W to start burner and G for fan in some systems.

To use the boiler transformer for thermostat C it must be the same lead that goes to directly boiler's activating relay coil.

A problems can arise when too many things are connected to boiler transformer OR the correct lead is not used for C to other systems.

To avoid problems I use one 24 VAC transformer for everything: 8 zone valves, circulator relays, electric stack vents, etc.
Old 10-06-19, 11:27 AM
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Welcome to the forums.

Look closely at your owners manual. It should specifically state that a relay must be used with three wire zone valves. Four wire zone valves are not affected.

You won't need a zoning panel for two zones but you will need a separate 24vAC 40va transformer and a 24v relay.

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