Furnace Tune-Up Checklist: What a Tech Does and What You Can Check Before Heating Season

A furnace tune-up is a systematic inspection and cleaning of your heating system, done once a year before you actually need the heat. A tech typically spends 45 to 90 minutes on it. Here’s what happens during that visit, and what you can check yourself before they arrive.

What the Tech Actually Does

The inspection follows a logical order: start at the thermostat, work through the air system, then the combustion side.

Thermostat and controls. The tech confirms the thermostat calls for heat correctly, checks the wiring connections, and verifies the fan cycles on and off as it should. If you have a smart thermostat, they’ll confirm the heat and aux stages are configured right.

Filter. This is the one thing homeowners can and should do themselves. A clogged filter restricts airflow, which makes the heat exchanger run hot, which shortens its life. Most 1-inch filters need replacing every 1 to 3 months during heating season. If the tech finds a gray brick where a filter used to be, expect a conversation.

Blower motor and belt (if applicable). The tech checks that the blower spins freely, measures amp draw to catch a motor that’s working harder than it should, and lubricates bearings if they’re the oil-port type. Older belt-drive systems get the belt tension checked as well.

Heat exchanger. This is the most important safety check in the whole visit. The heat exchanger is the metal barrier between combustion gases and your house air. If it cracks, carbon monoxide can mix into the air you breathe. The tech inspects it visually, sometimes with a mirror or camera, and may run a CO test downstream. Cracks often show up as soot streaking or a visible fracture line. If there’s any doubt, they may use a combustion analyzer or tracer gas to confirm.

Burners and ignition. The tech pulls the burner assembly, cleans off dust and debris, checks the flame pattern (should be mostly blue, not yellow or lifting), and inspects the hot surface ignitor for wear. These ignitors degrade over time and a cracked one is a common pre-season find. Catching it at a tune-up is a much better situation than having it fail on a cold morning.

Flue and venting. They check the flue pipe for corrosion, blockages, or disconnected joints. A blocked or leaking flue is another CO risk. On high-efficiency furnaces with PVC venting, they’ll look for cracks or improper slope that could cause condensate pooling.

Gas valve and manifold pressure. With a manometer, the tech verifies the gas pressure matches the furnace specs. Too low and the furnace short-fires; too high and you’re stressing the heat exchanger. Always checked against the data plate, not a generic target.

Safety controls. The limit switch, pressure switches, and rollout switches get tested. These are the controls that shut the furnace down if something goes wrong. The tech checks continuity and operation with a meter to confirm each switch opens and closes at the right point in the cycle. A rollout switch that has tripped is not something to reset and ignore; it points to a real problem that needs diagnosis.

Combustion analysis. On the thorough visits, a tech will stick a probe in the flue and read carbon monoxide, carbon dioxide, and oxygen levels. This tells them how efficiently the furnace is burning and whether combustion is complete.

What You Can Check Before They Arrive

A few things you can do the day before that make the visit go smoother and help you have a better conversation with the tech:

• Replace or at least inspect the filter. Note the size and what you find (gray with dust, or still white).
• Clear the area around the furnace. Two feet of clearance is standard; move any storage.
• Make sure the furnace kicks on when you raise the thermostat. If it doesn’t even start, note what you see or hear.
• Check your carbon monoxide detectors. Replace batteries if they’ve been in more than a year.
• If you have a high-efficiency furnace with a condensate drain, look for standing water around the drain line.

You don’t need to diagnose anything. But showing up informed means you’ll understand what the tech tells you.

What You Should Leave to the Tech

Gas valves, heat exchangers, and anything involving the combustion system are not DIY territory. The stakes are high and the failure modes (gas leaks, CO exposure) are serious. Same goes for electrical work inside the furnace cabinet if you’re not already familiar with how to kill power safely.

Cleaning the burners yourself is technically possible but not worth the risk of disturbing a gas connection you’re not sure about. Let the tech handle it.

When to Call a Pro

Tune-up timing: before heating season starts, ideally September or October in the Bay Area before nights get cold. Don’t wait until the first time you actually need heat.

Call sooner if you notice: yellow or flickering burner flames, soot around the furnace cabinet, a burning smell the first few times you run heat (some dust smell is normal; persistent burning isn’t), the furnace short-cycling (turning on and off every few minutes), or any CO detector alarm.

An annual tune-up costs less than most repairs it prevents, and it gives you documentation that the system was serviced if a warranty question ever comes up.

If you’re in the Bay Area and want someone to run through this checklist on your system, we cover most of the region with same-or-next-day scheduling. You can book at bayareahvacservice.com.

Key takeaways

• A tune-up covers thermostat, filter, blower, heat exchanger, burners, flue, gas pressure, and safety controls.
• The heat exchanger inspection is the most important safety check: cracks can allow CO into your home air.
• Replace or inspect the filter before the tech arrives; it's the one thing you should always handle yourself.
• Schedule before October in the Bay Area so you're not calling for emergency service on the first cold night.

Related questions

Written by Andrew Kuznetsov. Andrew is the founder and owner of Bay Area HVAC Service (ADRIUM Service Solutions). He holds a California Contractor License (CSLB #1136642), EPA 608 certification, and completed factory training at the Daikin/Goodman plant in Houston in 2025. He writes from direct field experience, not marketing copy.

Further reading

• Mitsubishi Hyper-Heat (H2i): How It Keeps Putting Out Heat When It Gets Cold in the Bay Area , Most people think heat pumps quit when it gets cold. Mitsubishi's Hyper-Heat (H2i) line is built to keep working as temperatures drop, which matters more here than folks expect, especially on cold mornings and up in the East Bay hills.
• Mitsubishi Mini-Split Blinking a Fault Light? What It Means and What to Do , A blinking light on your Mitsubishi indoor head is the system telling you something is wrong. Here is what the blink pattern means, the checks you can safely do yourself, and when to bring in a factory-trained tech.
• Why Your Mitsubishi Mini-Split Is Leaking Water Inside (and How to Fix It) , A Mitsubishi mini-split dripping water inside almost always comes down to condensate that can't drain. Here's what causes it, the safe checks you can do yourself, and when to call a tech.