error Honeywell

Error Code Heating or cooling system does not respond

HVAC system fails to activate when thermostat calls for heating or cooling.

? What Causes This

Incorrect mode setting, setpoint below/above room temperature, power loss, furnace door open, or system not responding.

Press Mode button to set Heat mode and verify desired temperature is higher than room temperature.
Press Mode button to set Cool mode and verify desired temperature is lower than room temperature.
Check circuit breaker and reset if necessary.
Verify heating & cooling system power switch is on.
Ensure furnace door is closed.
Wait 5 minutes for system response.

Source: page 10 of the official manual

From the manual

This error code appears in: