By Alexander Georges · Last updated April 26, 2026

HVAC Repair Checklist

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Diagnose

Identify the exact symptom

Is it no heat, no cool, weak airflow, strange noise, bad smell, or short cycling? Pinpointing the problem saves time.

Check the thermostat display

Is it blank, flashing, or showing an error code? A dead thermostat is the #1 false alarm for HVAC failure.

Inspect the circuit breaker

Flip the HVAC breaker off, wait 30 seconds, flip back on. A tripped breaker is a quick fix that mimics a dead system.

Check the air filter

A clogged filter causes 80% of HVAC service calls. Pull it out and hold it up to light, if you can't see through it, replace it.

Verify all vents are open

Walk the house and confirm every supply and return vent is open and unblocked by furniture, rugs, or curtains.

Thermostat

Replace thermostat batteries

Most thermostats use AA or AAA batteries. Dead batteries cause blank screens and lost schedules.

Check thermostat settings

Confirm it's set to HEAT or COOL (not OFF), fan is on AUTO, and the target temperature makes sense.

Test with a manual override

Set the temp 5 degrees above or below room temp and wait 5 minutes. You should hear the system click on.

Inspect thermostat wiring

Remove the cover and check for loose, corroded, or disconnected wires. Loose connections cause intermittent failures.

Airflow

Replace the air filter

If the filter is dirty, replace it now. Use the correct size (printed on the old filter's frame) and the right MERV rating.

Clean supply and return vents

Vacuum dust and debris from all registers. Blocked vents cause pressure imbalances and hot/cold spots.

Check for ductwork leaks

Inspect visible ductwork in basement or attic for disconnected joints, holes, or crushed flex duct.

Clear the area around the indoor unit

Remove boxes, stored items, and debris within 3 feet of the furnace or air handler for proper airflow.

Inspect the blower motor

Listen for the blower fan. If the system turns on but no air comes out, the blower motor may have failed.

Cooling

Clean the outdoor condenser unit

Hose off dirt, leaves, and debris from the condenser fins. Blocked fins reduce cooling capacity by up to 30%.

Clear 2 feet around the outdoor unit

Trim bushes, remove leaf piles, and ensure nothing blocks airflow around the condenser.

Check the condensate drain line

A clogged drain causes water backup and can shut down the AC via the safety float switch.

Inspect the evaporator coil for ice

If the indoor coil is frozen, turn the system to FAN ONLY for 2-4 hours to thaw. Ice means low airflow or low refrigerant.

Heating

Check the pilot light or igniter

For gas furnaces: is the pilot light lit? For newer models, listen for the igniter clicking. No ignition = no heat.

Inspect the gas supply valve

Verify the gas valve near the furnace is in the ON position (handle parallel to pipe). Turned-off valves are a common oversight.

Check the furnace safety switch

The furnace door has a safety switch, if the panel isn't seated properly, the furnace won't run.

Look for furnace error codes

Most furnaces have a blinking LED on the control board. Count the blinks and check the code chart on the panel door.

Noises

Diagnose rattling or vibrating sounds

Loose screws, panels, or ductwork cause rattling. Tighten what you can access safely.

Investigate squealing or screeching

A worn belt or failing bearing causes squealing. Turn the system off to prevent further damage and call a tech.

Address burning or musty smells

Burning smell on first use of season is normal (dust burning off). Persistent burning or electrical smell means shut off immediately.

Check for banging sounds in ductwork

Popping or banging when the system starts is often duct expansion. Loud banging may indicate a delayed ignition problem.

Call a Pro

Know when to call a professional

Refrigerant issues, gas leaks, electrical faults, and compressor failures require a licensed HVAC technician.

Get multiple repair quotes

For non-emergency repairs, get 2-3 quotes. Prices vary widely, $150 to $500+ for the same repair.

Decide: repair or replace?

If your system is 15+ years old and the repair is over 50% of replacement cost, replacing is usually smarter.

Schedule preventive maintenance

Annual tune-ups ($75-200) catch problems early and extend system life by 5-10 years.

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