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

First, press the SYSTEM button to set the system to Heat or Cool (ensure temperature is set higher than inside temperature for heat, and lower for cool). Then check the circuit breaker and reset if necessary, ensure the power switch at the heating and cooling system is on, verify the furnace door is closed securely, and wait 5 minutes for the system to respond.

From the official Honeywell Focuspro TH5220D Thermostat manual, page 5

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