Honeywell thermostat replacement.
About this video
How to change a Honeywell thermostat and install wiring on a new Trane - Honeywell home thermostat. It's easy to replace a thermostat yourself. The blue wire typically goes into the "C" terminal. If no "C", the wire could be attached to a "B" terminal. But read the installation instruction first.
If you decide to follow this video, please do it at your own risk.
Related article summary
The article lists common causes and step-by-step fixes for a Honeywell thermostat heat not working on Auto, including low battery, software/configuration issues, wiring, furnace or sensor faults, and blower problems. Recommended actions include restarting/resetting the thermostat, checking wiring and auto/heat settings, programming schedules, updating or resetting firmware, inspecting the furnace limit control, replacing a faulty sensor, cleaning filters/igniter, and calling an HVAC professional or support if needed.