If your furnace fan is running but the house is not warming up, check when the air feels cold and whether the thermostat is calling for heat. That description helps you decide what to check and what to tell a contractor.

For Utah homeowners, the useful question is whether heat returns normally or the home keeps getting colder. If it keeps getting colder, request furnace repair from Larsen Heating and Air after the safe checks below. You do not need to identify a failed part before asking for help.

Gas odor or a CO alarm comes first

If you smell rotten eggs or sulfur, or suspect a gas leak, leave immediately. Do not use switches, appliances, electronics, or a phone in the affected area, and do not search for the leak. From a safe location, call your gas utility or 911. For Enbridge Gas customers in Utah, the gas emergency number is 1-800-767-1689. Follow Enbridge’s gas-leak instructions.

If a carbon monoxide alarm sounds, move everyone outside to fresh air and call 911. Do not look for the source or reenter until emergency responders permit it. CPSC’s CO guidance also says to get outside immediately if you suspect CO poisoning, even without an alarm, and call the fire department from a safe location. These situations take priority over a service appointment.

Notice when the air feels cold

Describe the pattern before changing settings:

  • Only at startup: Air may feel cool briefly before heated air reaches the room. Check your model’s normal startup behavior in the owner’s manual; there is no single waiting time for every furnace.
  • Between heating cycles: A fan set to ON may circulate room-temperature air while the furnace is not heating.
  • Throughout a call for heat: The blower is moving air, but persistent lack of warmth needs further attention.

Carrier’s startup and thermostat explanation supports the first two patterns. Do not assume continuous cold airflow is normal just because the fan runs.

This guide focuses on airflow without useful heat. If nothing starts, describe it as a no-start problem. If heat repeatedly starts and stops, tell the contractor about that cycling pattern as well.

Check the thermostat without opening equipment

Confirm that the thermostat is set to HEAT, with the target temperature above the displayed room temperature. Check whether a schedule or temporary setting changed the target. If you want the fan to follow the heating cycle, select AUTO rather than ON, following your thermostat’s instructions. Carrier explains these thermostat checks.

Record what you changed and whether warmth returned. If the settings are confusing or the thermostat does not respond as expected, Larsen’s programmable thermostat service page is a useful next step. Avoid changing installer settings, wiring, or equipment configuration.

Look for an obvious airflow restriction

Check that room supply registers are open and return grilles are clear of furniture or other obstructions. A dirty filter can restrict airflow, allowing the furnace to overheat; a safety control may then stop the burners while the blower continues running. Bryant describes this filter and airflow mechanism.

If the owner’s manual identifies a homeowner-accessible filter location, follow its shutdown and replacement instructions. Use the specified size and compatible filter type, as Carrier’s filter-replacement guidance explains. If access requires opening a burner or electrical compartment, leave it to a technician. Do not operate the furnace without a filter or bypass a safety switch.

A filter change is not proof that the underlying problem is resolved. If cold air continues or returns, request diagnosis rather than repeating shutdowns and restarts.

Why the fan can run when the heat has stopped

Beyond thermostat settings and airflow, possible causes include ignition failure, a flame-sensing problem, or another equipment fault. A flame sensor that cannot confirm a flame can cause the burners to shut down. These are possibilities for a technician to investigate, not conclusions you can draw from air temperature alone. Bryant explains ignition and flame-sensor causes.

Keep furnace panels closed. Leave ignition, gas, electrical components, and safety controls to a qualified HVAC professional. The homeowner checks here do not include relighting pilots, cleaning flame sensors, adjusting gas valves, or repeated resets. CPSC cautions against servicing fuel-burning equipment without the necessary knowledge, skill, and tools.

What if only one room feels cold?

Compare the affected room with another nearby supply register without removing grilles or entering an attic or crawlspace. Note whether the room has weak airflow, cool airflow, or both. Leaking or restricted ducts can reduce delivered heat and contribute to uneven comfort; that is a different observation from every register staying cold. Bryant explains the limits of ductwork as a cold-air explanation. For a problem concentrated in particular rooms, use Larsen’s uneven heating and cooling guide to organize a room-by-room comfort assessment.

Give the contractor a useful problem description

Use this short record when requesting service:

  • Thermostat mode, fan setting, room temperature, and target temperature.
  • Whether air stays cool, becomes warm briefly, or feels cool only between cycles.
  • Whether the issue affects all checked rooms or a particular room.
  • When it began and whether it followed a thermostat change or filter replacement.
  • Any unusual sounds and any displayed fault message you can read without opening the furnace.
  • Furnace model information from an accessible label or your records, if available.

For example, “The thermostat is on HEAT and AUTO, the room is below the target, and air stays cool at several registers” gives the contractor more detail than “the heater is broken.” Use your own observations; do not run repeated test cycles to complete the record.

When requesting Larsen furnace repair, explain whether your home is losing heat and ask about appointment availability and diagnostic charges. Once the problem is corrected, discuss HVAC maintenance and tune-ups for the heating season. Preventive service and an active no-heat problem are different appointment needs; describe the symptom when you book.