Flame Sensor
A flame sensor tells the furnace control board that the burner flame is present.
What Flame Sensor means at home
The flame sensor is a small safety part that sits in the burner flame. If it is dirty, damaged, or not reading properly, the furnace may ignite and then shut down within seconds. Cleaning may help in some cases, but repeated flame-sensing problems can also point to grounding, burner, gas, or control issues — diagnosed during furnace maintenance or an emergency no-heat call.
What it connects to
Parent system
the gas furnace safety system
Flame Sensor is part of the gas furnace safety system. That tells you which side of the system a technician will usually test first.
Related components
burners, ignitor, control board, gas valve
These are the parts most likely to be checked with flame sensor. One weak part can make a nearby part look guilty, especially when airflow, water, heat, or controls are involved.
Connected problems
burner lights then shuts off, no heat, repeated furnace lockout
This is what you are likely to notice at home: burner lights then shuts off, no heat, repeated furnace lockout. Those clues are more useful than guessing at the failed part.
Maintenance relevance
flame sensor cleaning, burner inspection, combustion checks, tune-ups
This is where flame sensor cleaning, burner inspection, combustion checks, tune-ups matters. The goal is to catch dirt, water, electrical weakness, or airflow strain before the next hard-weather day.
When to call a technician
the furnace lights for a few seconds and then shuts itself down
Schedule service when the furnace lights for a few seconds and then shuts itself down. At that point the issue usually needs measurements, not another thermostat setting change.
Questions homeowners ask about Flame Sensor
What does flame sensor mean in HVAC?
A flame sensor tells the furnace control board that the burner flame is present.
Can a homeowner fix a flame sensor problem?
You can check the thermostat, replace a dirty filter, make sure vents are open, and look for water or ice. Stop before sealed panels, wiring, refrigerant, gas, combustion parts, or safety controls.
When should I call about flame sensor?
Call when the problem changes comfort, airflow, safety, water, ice, odor, noise, breakers, or how often the system starts and stops. Tell the technician what changed before you try to name the part.