What temperature ranges can I set for heating and cooling on the TH5110D?
The acceptable temperature setting range for Heat is 40°F to 90°F (4.5°C to 32°C), and for Cool it is 50°F to 99°F (10°C to 37°C). If your temperature settings do not appear to change, verify that your desired temperature falls within these ranges. (Page 11)
From the official Honeywell TH5110D Home Programmable Thermostat manual, page 11
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