A short checklist to run through in autumn so the first cold night isn't the one that finds the fault.
Run it before you need it
Turn the heating on for 20 minutes on a mild autumn day. Listen for new noises, check that every outlet delivers warm air and watch for lockouts. Discovering a fault in April is far better than in July.
Replace the filters
Return-air filters accumulate a summer's worth of dust. Restricted airflow is the leading cause of overheat lockouts and it wastes gas continuously.
Clear the vents and flue
Check that furniture and rugs aren't covering floor outlets, and that the flue terminal outside is clear of nests and vegetation.
Check the thermostat
Compare the controller reading against a separate thermometer in the same room. A controller reading two degrees high will quietly cost you all winter.
Book the service
Then book a professional service including a carbon monoxide test. Autumn appointments are easier to get and cheaper than an emergency winter callout.