Furnace won't turn on? Check these in order

Short answer: Start with the thermostat (set to HEAT, a few degrees above room temperature, fresh batteries). Then check the furnace power switch and breaker, that the front door panel is shut tight, the filter, and the gas valve. If the furnace still won't start, read the blinking light code and call a pro.

Safety first: Smell gas? Leave the house and call your gas company from outside (Enbridge Gas in Utah), or call 911. Don't use the thermostat or light switches.

Step 1: Thermostat

Set it to HEAT and raise it 3 to 5 degrees above the room temperature. Replace the batteries if it has them. A blank screen means no power. Smart thermostats can also lose their Wi-Fi schedule or common-wire power.

Step 2: Power switch and breaker

Most furnaces have a switch on or near the unit that looks like a regular light switch. People flip it off by mistake. Then check the breaker panel for a tripped furnace breaker. If the breaker trips again right away, stop and call a pro.

Step 3: The door panel

A safety switch keeps the furnace off when the blower door isn't seated. Push the lower panel firmly into place.

Step 4: Filter

A badly clogged filter can make the furnace shut itself off for safety. Replace it.

Step 5: Gas

Make sure the gas valve to the furnace is open. If your stove or water heater also has no gas, call the gas company.

Step 6: Vents and drain (high-efficiency furnaces)

Check the white PVC pipes outside for snow, ice, or debris. Inside, a full condensate trap or kinked drain hose can keep the furnace from starting.

Step 7: Read the code

Look through the small window in the lower panel for a blinking LED. Match it to the chart inside the door. Common codes point to the pressure switch, igniter, flame sensor, or limit switch.

If it hums, clicks, or starts and stops

Clicks but never lights: igniter or gas supply.
Lights, then shuts off in a few seconds: flame sensor.
Inducer fan runs but nothing else happens: pressure switch or blocked venting.
Runs a few minutes, then shuts off: overheating (filter, closed vents) or a failing limit switch.

If the tech says an older furnace needs a major part, compare the repair quote with what a new furnace costs installed.

Went through all seven steps? Write down the blinking light code, then Request furnace help. One local heating company that serves your ZIP will contact you.

FAQ

How do I reset my furnace? Turn the power switch off, wait about 30 seconds, and turn it back on. Some models also have a reset button on the blower motor. If it keeps needing resets, call a pro.

Is no heat an emergency? In a Utah winter, it can be. Pipes in exterior walls can freeze. If it's below freezing and you can't get heat back, call for same-day service and open cabinet doors under sinks on outside walls.

Live in Salt Lake or Utah County?

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