Honeywell RTH8580WF hooking up to a Taco SR504


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Old 10-11-15, 05:32 PM
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Honeywell RTH8580WF hooking up to a Taco SR504

Just purchased a Honeywell RTH8580WF Thermostat and am trying to attach it to the Taco SR504-EXP. I ran a new 18-3 cable from the thermostat to the furnace. I connected the red wire to the R on the thermostat which has a jumper to RC. and the white wire to the W on the thermostat and finally used the green for the C connection. On the furnace replaced the R and W wires with the new wires Red and white, Ran the green to the com side of the 24v connection and no power to the thermostat, plugged it into the 24v side and it will cycle on then off. really need help on this.
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Thermostat connections

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Taco SR504-EXP connection
 

Last edited by Marc Weymouth; 10-11-15 at 05:57 PM.
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Old 10-11-15, 06:25 PM
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Welcome to the forums.

That Taco controller was not intended to be used with powered stats.

At the 24vac power port...... is it labeled C and 24vac ?
How did you determine which terminal to put red and white on as they aren't labeled ?
Do you have a meter ?
 
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Old 10-11-15, 07:55 PM
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Just to add to my prior post.

You have the red and white wires connected to TT. There is no polarity indicated there.

Disconnect the two wires on TT.
You'll need to check from the C terminal at the 24v power port to either TT terminal.
When you read 24vac between C and one of the TT terminals...... that T terminal is R.
Connect the red there. The other will be the white wire.
 
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Old 11-13-15, 10:09 AM
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Marc, did you find a solution to this? I am having an identical problem with the Taco SR-503 and a honeywell 6580 wifi thermostat. I can get it to power on using the R, W, and hooking the C into the 24vac on the Taco, but once I try to turn the heat on, it begins to flash on and off. I think I might need to return this thermostat.
 
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Old 11-13-15, 01:58 PM
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Welcome to the forums.

It sound like the W and R may be backwards.
Did you use a voltmeter and follow my testing method ?

It is imperative to determine the correct connections before connecting the stat to eliminate a shorting issue.
 
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Old 11-13-15, 05:16 PM
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Leave R and W from the Stat on the SR504 R&W terminals ,if you have a volt meter check between the R at the control and the 24 VAC terminals on the control ,which ever terminal gives you 24 volts connect your green wire there and the other end to the C terminal on the Stat,you should now have 24 volts between R&C.
 
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Old 11-17-15, 06:28 AM
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Thanks!

Thanks everyone! Yes the R and W were reversed! When they are reversed, it's possible to power up the thermostat if you run the C wire into the 24VAC terminal on the Taco SR503, but it will blink on and off as you try to engage the heat. Switching the R and W on their TT hook ups and connecting the C wire to the Com terminal, I was able to solve this issue. Cheers everyone!
 
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Old 11-17-15, 10:25 AM
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Awesome news.

If you could..... let me know which terminal is which so I know for future reference.
R and W..... left / right
 
 

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