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Old 02-02-2011, 03:55 AM   #1
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Old Wall Thermostat to New Digital Thermostat Problem


I just purchased a Honeywell RTH221B thermostat to replace my old Robertshaw 500-107R thermostat. This is for a gas heater only in an old 1920s apartment building.

There were only 2 wires connected the Robertshaw, one in the O terminal and one in the X.

The Honeywell instructions say to connect the O to the terminal which is fine and to leave the X disconnected. Simple enough.

However, with only the O wire connected, the heat doesn't come on. What am I doing wrong here? Thanks.

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Old 02-02-2011, 04:42 AM   #2
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Old Wall Thermostat to New Digital Thermostat Problem


Need to connect both wires. Use RH and W.

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Old 02-02-2011, 05:00 AM   #3
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Old Wall Thermostat to New Digital Thermostat Problem


Thank you so much, beenthere! Just connected the former O terminal to R/RH and the former X terminal to W and it works! I never would have figured that out. You just saved me from a cold Los Angeles night
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Old 02-02-2011, 05:07 AM   #4
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Old Wall Thermostat to New Digital Thermostat Problem


Your welcome.
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