Setting up new smart tstat with newly installed Tstat line Weil McLain Cga

J_D65

Hope all is well. I bought new smart tstats which require a common wire. I soon realized I didn’t have a common line. I only had a red and white with a jumper between RC and RH.  I ran a new wire from my upstairs and downstairs zone to the furnace. That was a treat. New line has three lines, red, white, green. I then connected the red and white from the new lines to the furnace the same as the old lines were. I looked at the furnace electrical and there was a wire labeled C not being used. I connected the C to the new green tstat lines. I tried the new tstats and there was no power. I then setup the old tstat using the common to see if maybe the new tstats were bad. Old tstats didn’t work either. Currently running on the new lines but using the old tstats with the original AA battery config. 

So I’m trying to avoid calling the hvac company because I feel I’m almost there but maybe not. I took pics and typed out where everything goes. 

Within the furnace the black labeled tstat  connect to a red and white. These red and white go to front of valve #2.  Valve 2 has jumpers over to valve #1

Blue DHW from furnace connect to red and white that connect to the top of valve that goes to hot water storage tank. 

Transformer has a green, red and white connected to R and a white connected to C. 

Green from R transformer connects to TR on water storage valve.  White from transformer R connects to #2 valve at TR. 

Red from transformer R connects to TR on valve #1. 

White from wall tstats and water tank connect together to a splice to C on transforme.

R and C labeled wires coming from furnace electrical not being used. 

I figured I would ask here before throwing in the towel.  I was thinking maybe I could connect the common wire from the tstats to the transformer at C but I didn’t want to cook anything. Thanks again. 

Jamie Hall

Have you tried simply reversing the red and white wires at the thermostat? Better (and safer), if you have a multimeter, see which one reads 24 volts with respect to your C wire with the thermostat off or disconnected. That is the one which is "red" -- regardless of which colour it is.

EdTheHeaterMan

Sometimes the wiring of zone valves with a 2 wire thermostat will work just fine, but when you need to add a common wire the R and the C on the transformer are reversed. When this happens the EASY to Install C wire is not so easy.


By reversing the wiring and making sure that the R from the transformer goes to R on the thermostat everything else falls into place just fine. It is important for the transformer R goes to the Thermostat R as in the following illustration



In the Honeywell wiring diagram they do not specify which is R and C and W because it does not matter when using a 2 wire thermostat R and W can ve swapped because they are just switch legs to the valve motor.

When the thermostat ALSO needs a common wire then you MUST place transformer R on thermostat R in order to use the transformer C for both the thermostat C and the and the zone valve motor C. If your systems is wires backwards, then it is usually easiest to swap the C and R at the transformer, but sometimes it mist be swapped at the thermostat W and R.
WARNING: What ever you do with one zone valve, you must do the same with all the zone valves. or you may damage the transformer. then you will have NO HEAT at all

I like to use a fuse on the transformers. It keeps the Factory Installed Smoke inside the transformer if you mess up!

J_D65

Thanks. So based on the diagram woukd i be connecting a wire from R on transformer to Th-Tr on each zone valve  and also connecting each thermostat R wire to Th-Thr on their corresponding zone valve? Thanks 

EdTheHeaterMan

J_D65 said:

Thanks. So based on the diagram woukd i be connecting a wire from R on transformer to Th-Tr on each zone valve  and also connecting each thermostat R wire to Th-Thr on their corresponding zone valve? Thanks 

YES to be sure you get it correct. But so you know... The terminal Th/Tr is not connected to anything inside the zone valve actuator. That terminal is just an easy place to put two wires. Think of it as a wire nut hanging in the air. It just looks a little nicer.