Question about Honeywell Electronic Programmable Heat/Cool Thermostat - CT3300A100 Heater

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How do I calibrate the temperature for the RTH7500D thermostat? It is 2 degress warmer than the thermostat reflects. Does this thermostat operate on the battery power alone? There are only two wires going to the thermostat. One is the red hot and the other is the return leg that activates the relay that transfers power to the hot water pump that circulates water to the registers. .Since there is no common wire going to the thermostat and the thermostat will not operate without the batteries, I am assuming the battery is the only source of power that operates the thermostat.

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  • Melvin71 Dec 04, 2008

    The second part of my question was not answered. Does the 2 AA batteries provide power for the RTH7500 thermostat since there is no neutral wire(X terminal) going to the stat. There is only the hot (R terminal)and return wire(W terminal) to activate the heat.. I am guessing that the hot wire and the wire to the W terminal provides 24v power to the thermostat but if that is the case, why does the stat show no display when no battery power is present?


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There is no feature in this thermostat to adujust sensor. You need to make sure you have picked for hot water systems.

Follow blue link for instruction manual

If you need more information, please post back.
If this answers your question please hit accept

Posted on Nov 28, 2008

  • Joseph Lillie
    Joseph Lillie Dec 04, 2008

    Yes the battery supply the power for the thermostat


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