Furnace flame sensors are a critical heating safety component. This device verifies that the main furnace-burner flame has ignited properly after the thermostat signals for heat. The electrical signal from the thermostat opens the gas valve and an electronic igniter lights the burner. If every step in this process functions correctly, then the furnace produces heat safely.
However, if something goes wrong and the burner fails to ignite, unburned natural gas could continue to flow, escaping into the house and posing a serious safety hazard due to potential fire or explosion. Read on to learn how flame sensors prevent that from happening to keep you safe.
Flame Sensor Basics
The flame-sensing rod that reacts to heat extends into the furnace burner. The sensing rod is connected to the furnace's electronic control board.
The control board receives a signal from the thermostat and opens the main gas valve, then actuates the electronic igniter that lights gas flowing into the burner.
If the burner flame ignites, heat produced by the flame is detected by the sensing rod. The control board allows the gas valve to remain open, and heat is produced safely.
If the sensor does not detect the burner flame, the furnace control board shuts off the gas valve immediately.
Potential Flame Sensor Issues
Sensor-detection function can be affected by a number of issues, most of which are related to the age of the component. A frequent telltale symptom of a failing sensor is that the furnace "short cycles." It starts up properly when signaled by the thermostat but then almost immediately shuts down again. The furnace will not continue running beyond a very short time.
Common causes of sensor failure include:
Cracked, bent, or broken sensor rods
A dislodged sensor rod
Carbon residue on the sensor that is degrading heat-sensing capabilities
Annual furnace maintenance by a certified HVAC technician helps prevent sensor problems, as well as detect and diagnose a failing sensor.
For experienced service to diagnose and repair flame-sensor problems, contact the heating professionals at Air Assurance.