If you don't feel comfortable performing any of the actions listed below, please don't attempt to. Reach out to a friend or family member that is more familiar and willing to help.
Avoid Temu and gibberish brands from Amazon. This is one area where you do not want to cut corners.
Make sure your smoke/fire alarms are functional and that your fire extinguishers aren't expired.
If you have fuel burning appliances. and you don't have a Carbon Monoxide (CO) detector, get one for each level of your home (look for "Low Level" on the label). Follow the manufacturer's instructions for installation. Bonus: Get an explosive/combustible gas alarm too.
Preferably after you've performed the visual inspections listed below, but before it gets cold enough that you need your heat to work, test your unit now. Please confirm the sequence of operations in the user manual. Generally, you can set your thermostat to HEAT and at least 3 degrees ABOVE the current room temp to make sure the unit fires up properly.
*IMPORTANT SAFETY NOTICE: Do not take the doors off the furnace or boiler while it is running.
Please confirm the shutdown procedure in the user manual before performing maintenance. Generally, this involves switching your thermostat to OFF (and fan to auto), flipping the emergency power switch (or breaker). For long-term shutdowns, it may also include shutting off the gas but that typically isn't necessary for a short-term shutdown during an inspection.
*Refer to safety notice above
Ensure all supply registers and return vents throughout the house are open and unobstructed by furniture or rugs to maintain proper static pressure.
Air Filter: Inspect and change your air filter (1" to 3" filters should be checked monthly to every 6 months depending on thickness and pet situation). Write the date changed on the end of the filter in permanent marker. Wipe down any dust inside the blower door and make sure the door safety switch closes flush.
Burner Flame: Look through the sight glass during a call for heat to confirm a crisp, steady blue flame. Yellow or flickering flames mean dirty burners or airflow issues. If you don't have a view port, with doors on, verify you hear the burners engage, and if you have a furnace, confirm that you feel warm air at the registers.
Burner Flame Rollout, critical issue: Flames reaching or spilling out from the front of the burner compartment indicate a severely blocked flue, clogged heat exchanger, or draft failure.
Flue Pipe (Metal): Look over the metal exhaust pipe for rust, loose clamps, or soot build-up near the draft inducer fan. If there are any holes in your exhaust pipe, that's a serious problem and don't let anyone tell you otherwise.
Flue Pipe (PVC): Look over the PVC exhaust for cracks, water leaks, and discoloration. The exhaust should also have a consistent slope back towards the furnace, look for sagging between hangers. Condensation forms in the exhaust pipe and it is designed to drain at the furnace.
Combustion airflow: Identify where the exhaust/intake pipes are exiting the house. Go outside and verify the pipe terminations are clear of obstructions to maintain proper intake and exhaust airflow. This is also important after any snow storm.
Relief Valve: Check the floor under the Temperature/Pressure Safety Relief Valve discharge pipe for active drips or moisture.
Flue & Venting: Look for rust flaking, corrosion, or soot around the draft hood and chimney connection. If there are any holes in your exhaust pipe, that's a serious problem.
Circulation Pump: Listen for grinding or strange noises in the hot water pump and check for active seal leaks around flanges.
Wiring: With the furnace OFF, remove the cabinet doors and visually inspect wiring connections for signs of overheating, charring, or melted wire insulation near the heat sequencers and heating element banks.