Thermostat - no image on display screen

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?
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.
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.
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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