What should I do if my heating or cooling system does not respond?

First, make sure the SYSTEM button is set to Heat or Cool and that the temperature is set above or below the current inside temperature accordingly. Also check that the circuit breaker is not tripped, the power switch at the heating and cooling system is on, and the furnace door is closed securely. After checking these items, wait 5 minutes for the system to respond. (Page 19)

From the official Honeywell TH6110D Programmable Digital Thermostat manual, page 19

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