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Furnace not turning on or blowing cold air? Safe checks first

General home information from Prufloop. Updated October 28, 2026.

What you can safely check

• Set the thermostat to Heat and a few degrees above room temperature. Replace its batteries.
• Replace a dirty filter. A clogged filter can make the furnace overheat and shut down.
• Check the furnace power switch and the breaker.
• Make sure the blower compartment door is seated; a safety switch keeps the furnace off if it isn't.
• Look through the small window on the furnace for a blinking light and write down the pattern for the tech.

When to call a HVAC tech

• The furnace tries to light and shuts off
• You see a repeating error code
• You hear booms when it lights, or see soot
• Any carbon monoxide alarm or gas smell (after calling the gas utility)

What a HVAC tech will usually do

• Tests the igniter, flame sensor and gas valve
• Checks venting and the heat exchanger
• Reads the control board's error codes

Asking an AI assistant to book it

Once Prufloop launches (planned for Q4 2026 around Charlotte), you'll be able to ask the AI assistant you use something like this, and it can book a verified pro at a posted price in a real open slot. This is how it's planned to work; no assistant is connected yet.

Before a job is booked, you see the pro's posted price, including any trip or diagnostic fee. Anything extra needs your OK first. When the work is done, you confirm it's fixed with a quick text. That's Proof of Done™.

Questions

Related hvac problems

• AC running but not cooling?
• Ice on your AC lines or coil?
• Heat pump not heating?
• Thermostat screen blank?
• HVAC around Charlotte

This page is general information, not a diagnosis. Conditions vary by home. When in doubt, and always for gas, electrical or anything that feels unsafe, have a licensed professional inspect it.