What should I do if my heating or cooling system is not responding?

First, press the SYSTEM button to set the system to Heat or Cool (as needed), and make sure the temperature is set higher than the inside temperature for heating, or lower for cooling. Check the circuit breaker and reset if necessary. Ensure the power switch at your heating & cooling system is on and the furnace door is closed securely. Wait 5 minutes for the system to respond. (Page 5)

From the official Honeywell TH5220D1029 Thermostat manual, page 5

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