No Heat From Vents

'No heat from vents' can mean two very different things: (a) the system is running but you feel nothing at the registers, or (b) the system isn't running at all. The diagnostic path is different for each. Start by figuring out which you're dealing with.

Most Likely Causes

1. Tripped breaker or blown fuse (system isn't running)

If you hear nothing from the furnace or air handler, check the breaker panel. Gas furnaces still need power for the blower and control board. Electric air handlers pull significant current — breakers do trip. Flip both the furnace and air-handler breakers fully off then back on.

2. Furnace power switch turned off

Almost every furnace has a rocker switch — looks like a wall light switch — mounted on or near the unit. It's easy for someone to accidentally flip it during storage moves or cleaning. If your furnace is silent, check this switch first.

3. Thermostat dead or misconfigured (system isn't running)

If the thermostat screen is blank or unresponsive, batteries or the low-voltage fuse on the control board may be dead. If the thermostat is on but not calling for heat, verify: set to Heat mode (not Off or Cool), setpoint at least 3-5°F above current room temp, and the schedule/hold state is what you want.

4. Blower motor failed (system is running but no airflow)

If you hear the furnace kick on but nothing comes out of the vents, the blower motor may have failed. On modern ECM (variable-speed) motors, the motor module can fail while the motor itself is fine. Replacement runs $420-$780 for standard PSC motors, $800-$2,400 for ECM.

5. Failed transformer or blown low-voltage fuse

The 24V transformer powers the thermostat and control circuits. If it burns out or the 3-5 amp fuse on the control board blows (usually from a shorted thermostat wire, often rodent damage in the attic), everything looks dead. The fuse is a $1 part but you have to know to look.

6. Blocked or disconnected ductwork

If the system is running fine but only certain rooms have no air, you likely have a duct issue — crushed flex duct in the attic, a disconnected supply duct dumping air into the attic, or closed manual dampers. See our weak airflow guide for the full walkthrough.

Try These Steps Before You Call

• Check the thermostat: batteries fresh, set to Heat mode, setpoint above room temp, no hold overriding your setting.
• Check the furnace on/off switch (looks like a light switch, mounted on or near the furnace).
• Check both breakers — furnace and air handler — flip fully off then back on.
• Listen for any sound from the furnace/air handler with the thermostat calling for heat. Total silence = power/thermostat/fuse problem. Hearing something but no airflow = blower problem.
• Look for water in the condensate pan or a tripped float switch (kills power to the whole system).
• For pilot-light systems (rare now), see our pilot light won't stay lit guide.

Other Common Heating Problems

See also: AC problems