Furnace Tune-Up Checklist: What a Pro Actually Checks
When you schedule a furnace tune-up, you’re trusting a technician to evaluate a complex system that your family’s safety and comfort depends on through a long Minnesota winter. So it’s reasonable to want to know: what exactly are they doing in there?
A legitimate furnace tune-up isn’t just a quick look-over and a filter swap. It’s a methodical inspection and service of every major component in your heating system. Here’s the complete checklist of what Maverick’s Heating & Air technicians cover during a professional furnace maintenance visit, and why each item matters.
Safety Checks: The Non-Negotiables
These are performed first, because they relate directly to the safety of your household.
Heat Exchanger Inspection
The heat exchanger is the most critical safety component in your furnace. It’s a series of metal chambers that separate the combustion gases (including carbon monoxide) from the air that circulates through your home. A crack or hole in the heat exchanger can allow CO to enter your living space, a potentially fatal hazard.
What the technician does: Visual inspection of all accessible heat exchanger surfaces, often using a mirror and flashlight, and sometimes a camera for hard-to-see areas. Some technicians also use a CO analyzer to detect combustion gases in the airstream as a secondary check. If a crack is found, the furnace must be taken out of service until repaired or replaced.
Carbon Monoxide Testing
We check CO levels in the supply air coming from the furnace registers, and sometimes at the flue exhaust. Even a functioning heat exchanger can allow CO infiltration in some failure modes. This test provides an independent confirmation that your living space air is safe.
Flue and Venting Inspection
The flue pipe carries combustion gases from the furnace to the outside. We inspect:
- Flue connections for proper sealing, gaps allow CO to escape into the mechanical room
- Flue pipe condition, corrosion, holes, or disconnections
- Proper pitch, the flue must slope in the right direction for proper draft
- Flue termination, the outdoor exhaust point should be clear of obstructions, ice, and wildlife (bird nests are more common than you’d think)
For high-efficiency furnaces with plastic PVC venting, we inspect for any cracking, improper slope, or condensate blockages.
Gas Pressure and Valve Test
We verify that gas pressure at the furnace is within the manufacturer’s specified range, too low reduces heating capacity, too high is a safety concern. The gas valve itself is tested for proper opening and closing.
Emergency Shutoffs and Disconnect Testing
The furnace should have accessible emergency shutoffs. We verify they are functional and that the technician (and you) know where they are.
Combustion System: Getting the Burn Right
Burner Cleaning and Inspection
Over time, furnace burners accumulate dust, rust, and debris that cause uneven or incomplete combustion. Dirty burners:
- Waste fuel
- Can cause the furnace to struggle with ignition
- May produce more CO than a clean burner
What the technician does: Removes the burner assembly (on most systems) and cleans with compressed air and appropriate tools. Inspects the burner ports for blockages or corrosion.
Flame Sensor Cleaning
The flame sensor is a small metal rod that verifies the burner has actually lit. If it’s coated with oxidation (it always will be after a season of use), it can’t properly read the flame and causes the furnace to shut off after a few seconds, one of the most common service calls we receive.
What the technician does: Removes the flame sensor and gently cleans the rod with fine steel wool or emery cloth. This is a five-minute task that prevents a lot of “furnace won’t stay on” calls.
Igniter Inspection
Modern furnaces use a hot surface igniter (a silicon carbide or nitride element that glows orange-hot to light the gas) rather than a standing pilot light. Igniters are wear items, they become brittle and eventually crack.
What the technician does: Visually inspects the igniter for cracks or damage. Measures electrical resistance to assess remaining useful life. A weakening igniter often shows abnormal resistance readings before it fails completely. Replacing it at this point is much better than an emergency call on a cold night.
Combustion Analysis
On many service visits, we perform a combustion analysis using calibrated test equipment that measures O₂, CO, CO₂, and flue temperature in the exhaust gases. This tells us precisely how efficiently the furnace is burning and whether there are combustion problems that can’t be detected visually.
Mechanical Components: Keeping Things Moving
Blower Motor Inspection
The blower motor and fan wheel are what move heated air through your ductwork. Issues with the blower reduce heating efficiency and can cause the furnace to overheat.
What the technician checks:
- Amp draw, excessive draw indicates a motor under strain
- Bearings, listened for and felt; worn bearings create noise and eventually cause motor failure
- Capacitor (on single-phase motors), the capacitor helps start and run the motor; a weak capacitor is a common cause of blower failure
- Fan wheel cleanliness, a dirty blower wheel can lose 20–30% of its airflow capacity. Cleaning is often one of the most impactful things we can do.
Belt Inspection (Older Belt-Drive Systems)
Older furnaces use a belt between the motor and blower. We check:
- Belt tension (too loose slips; too tight stresses bearings)
- Belt condition (cracking or fraying)
- Belt alignment
- Belt replacement if needed (inexpensive preventive maintenance)
Modern direct-drive systems don’t have belts, but they still have bearings, capacitors, and motors that require inspection.
Electrical Connections
Heat and vibration cause electrical connections to loosen and corrode over time. Loose connections increase electrical resistance, which generates heat and can cause arcing, component damage, or fire. All electrical connections at the furnace are inspected, tightened, and treated with dielectric compound where appropriate.
Controls and Thermostat
Thermostat Calibration
Is your thermostat accurately reading and controlling temperature? We test the thermostat to verify it’s calling for heat at the correct temperature and that the furnace responds properly.
Limit Switch Testing
The high limit switch is a safety device that shuts the furnace off if it overheats. We test it for proper operation, an improperly set or failed limit switch can either allow dangerous overheating or cause unnecessary shutoffs.
Control Board Inspection
We inspect the control board (the brain of the furnace) for any error codes, signs of overheating, or visible damage. Most modern control boards display a blinking LED error code history, reviewing this gives us insight into any problems the furnace has experienced since the last service visit.
Airflow and Filtration
Filter Assessment
We check the filter condition and advise on the appropriate filter type and replacement schedule for your specific system. Not all filters are right for all furnaces, too restrictive a filter can cause as many problems as a dirty one.
Supply and Return Airflow Check
We verify that the furnace is moving an appropriate amount of air, measured in CFM (cubic feet per minute). Restricted airflow is one of the most common causes of efficiency loss, comfort problems, and equipment damage.
Duct Connection Integrity
We check the immediate duct connections at the furnace for gaps, leaks, or disconnections.
System Startup and Cycle Testing
After all individual checks and services are complete, we run the furnace through a complete heating cycle, confirming it starts, runs, and shuts off normally. We measure:
- Time to ignition
- Supply air temperature rise (the difference between return and supply air, should be in the manufacturer’s specified range)
- Steady-state operation
We don’t leave until we’ve confirmed the system is operating correctly.
After the Tune-Up: What You’ll Receive
At Maverick’s Heating & Air, we document everything from the tune-up, what was found, what was serviced, and any recommendations for repairs or upcoming replacements. You’ll know exactly what shape your system is in heading into the Brainerd Lakes Area heating season.
Book your fall tune-up today, let’s make sure your system is ready when the cold arrives.