Taco SR-502-4 C-wire

rc1020

Hi everyone,

I just purchased a Honeywell Wifi and trying to get the C-wire working. I have 18-6 cable to two zones and two thermostats. I only have heating controls, so the current setup in Zone 1 has just the "R" and "W" terminals connected at the current (old) thermostat (with Red and White wiring, respectively).

However, since it's 18-6 cable, i have four extra wires that i figure i can use as a C-wire (Blue, Yellow, Green, Brown) for the new Zone 1 Honeywell WiFi thermostat.

I've connected the Blue wire from the same Zone 1 18-6 cable to the "COM" terminal at the relay and to the "C" terminal at the thermostat, but the Honeywell did not power up.

I've confirmed with a multi-meter there is 24V+ between the "COM" and Zone 1 "R" terminals at the TACO relay. So, the terminal block is properly powered. But, using the multi-meter there is no power at the Blue wire at the Zone 1 thermostat. I tried the Yellow, Green and Brown wires as well to see if it was a wire issue, and same thing, no power for the C-wire.

I then tried swapping the four extra wires with the White wire at the "W" terminal on the TACO relay, and no power between "R" and "W" at the thermostat, which tells me that the four extra wires are cut off somewhere along its route and only two of the six wires have a complete circuit.

This to me seems odd. It's a new construction (2012), and so i don't see why the installer would chose to cut four of the six wires somewhere along the way.

Am i missing something?

thanks!

Paul48

I won't pretend to be able to follow what you've tried to do, but the "C" wire is a common, which is like your neutral in an outlet. The red and white wires at a thermostat are a switched circuit. They just pass 24 volts. Your wi-fi thermostat needs 24 volts to operate, so it needs red, white, and common. Electricians would probably cringe with that description, but its all I got.

PS......You can check the integrity of the wires in the walls by twisting 2 at a time together at the thermostat, and checking the other ends with an ohm meter.

rc1020

Ha, I suppose it was a bit of a long-winded ramble! I understand your point, very simply the issue is that of the 6 wires, only 2 seem to be able to complete the circuit (Red and White). I can't for the life of me figure out why the other four would be broken.

Thank you for the tip on checking wire integrity, that's a much smarter way to do it. It does confirm that the other wires aren't continuous.

Zman

Another possibility is that you have the polarity backwards. I would hook the thing up in the mechanical room (after verifying the polarity) and see if you have a wire issue or a wiring issue.
If the polarity is backwards, the taco unit won't care but the t-stat will....

Tinman

I had an issue with TH8320WF1029's a few years ago. I installed 6 of them in a heating cooling application - Space Pak and hydronic zones. It was critical that the C (common wire) from the stats was tied into the common of the cooling transformer.

Once I made the switch, everything worked.

I know yours is a heating only app. There may be something quirky about the wiring on that too? I'll see if I can find anything.

Tinman

I checked. No, pretty straight forward.

rc1020

If it was polarity, then at least I'd still get power to the wires (but agree the tstat wouldn't work). That's what I can't figure out, why 4 of the 6 wires aren't continuous. Seems odd an installer would randomly break them along the way.

hot_rod

Are the wires the exact same at both ends? If an installer runs short of wire and splices along the route, the conductors may look different at either end. Could be the colors are off a bit or the jacket around them is different?

rc1020

Jacket looks the same (can't be 100% sure) and colors are the same. I figure they did a splice like you say, but why they wouldn't splice all six wires is just crazy.

Tinman

Time to get the ohmmeter out and verify.

rc1020

Yep, all failed continuity.

RobG

That makes no sense. If all six wires failed on continuity the system would never have worked at all. Are you sure you have your MM set correctly?