Thermostat - no image on display screen


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Old 05-11-14, 04:03 PM
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Thermostat - no image on display screen

I'm installing a 7 day programmable Honeywell RTHL221B thermostat to replace an older analog Honeywell. There are only two wires for the control, a red one and a white one. Before doing anything to connect the wires I installed 2 AAA batteries as per the manual. There was no image on the display window. (I think there should have been.) With power off, I connected the white wire to the W terminal and the red wire to the R terminal. Then I turned on the electricity. There still was no image in the display window, so I couldn't proceed to program the unit. I exchanged the first thermostat with a new one, same model, same result. Anybody have a suggestion?
 
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Old 05-11-14, 05:08 PM
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First things first. Check that the batteries are inserted properly..per the manual. That seems the most likely issue.
 
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Old 05-12-14, 12:25 AM
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You need heat only stat. You have millivolt system. Get basic heat only stat it will only have red r and white w terminals and it works from millivolts. The standing pilot or spark ignitor generate energy this is millivolt energy it's enough to open gas valve then fan switch takes over.
 
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Old 05-12-14, 07:32 AM
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You need heat only stat. You have millivolt system.
I'm trying to figure how you determined that ????

Since there are only two wires it is a basic heating system. OP hasn't told us the type of heating system.
 
 

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