TAC thermostat (model 31-100) for Normally-open zone valve

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Old 03-08-11, 06:09 PM
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TAC thermostat (model 31-100) for Normally-open zone valve

My condo has a central boiler on top of the 12-storey building that feeds hot water to baseboard heater in each unit. There is a room thermostat that operates a zone valve to control the flow of hot water hence the heat.

Few months back the heat in my apartment was on all the time regardless of the thermostat setting. A repair guy sent by the building superintendent replaced the old parts with a TAC normally-open zone valve, a TAC modulating valve, and a TAC thermostat. After the repair, when I turned the thermostat to high, the heat would turn off (the zone valve closed); when I turned the thermostat to low, the heat would turn on (the zone valve opened). The repair guy and the superintendent refused to correct the situation saying that the heat can now be turned “on” and “off”.

Anyway, it seems to me that if I switch the wire in the thermostat from the “W” terminal to the “Y” terminal, my heating system would be working properly. The TAC thermostat is 24 Vac and has 3 terminals labelled “Y”, “R” and “W”. Right now there is a single wire each connected to the “R” and the “W” terminals. Please let me know if I am right. Thanks.
 
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Old 03-08-11, 07:23 PM
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I'm unfamiliar with this system. However, your logic makes sense to me.
 
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Old 03-08-11, 07:57 PM
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Originally Posted by hvactechfw View Post
I'm unfamiliar with this system. However, your logic makes sense to me.
Thanks. I am also thinking what is the difference between this set up and using a heat only reverse acting thermostat.
 
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Old 03-08-11, 08:05 PM
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correct that would be the same concept as using the Y terminal on your current stat. The current stat is a SPDT stat. Choosing Y is is just opening the circuit on temp drop instead of closing the circuit.
 
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Old 03-08-11, 08:12 PM
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Originally Posted by hvactechfw View Post
correct that would be the same concept as using the Y terminal on your current stat. The current stat is a SPDT stat. Choosing Y is is just opening the circuit on temp drop instead of closing the circuit.
so are you saying that it is the same as using a heat only reverse acting thermostat?
 
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Old 03-08-11, 08:13 PM
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yes. that is exactly what I'm saying.
 
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Old 03-08-11, 08:29 PM
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Originally Posted by hvactechfw View Post
yes. that is exactly what I'm saying.
Thanks. I will test it out and see. The only thing I am wondering is why then they want to make a "heat only reverse acting thermostat", if we can do without by doing it my way. From the web, I can see that the 2 are more or less the same price.
 
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Old 03-08-11, 08:38 PM
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because your thermostat is meant for heating or cooling. But it uses the same concept as heat only reverse acting. yours is heat only or cool only (heat only reverse acting)
 
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Old 03-09-11, 07:09 PM
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Originally Posted by hvactechfw View Post
because your thermostat is meant for heating or cooling. But it uses the same concept as heat only reverse acting. yours is heat only or cool only (heat only reverse acting)
Thanks for all your info.
 
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