Your Furnace Turns On and then Off Quickly
Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism. Except, there is a flame and without the gas to supply it, it dies.
There is a work-around to waiting. If there is no safety risk (like a gas leak), a furnace can be reset to bypass this wait. Turn off the furnace's power switch and wait 10 seconds before turning it back on.
So, when the flame sensor doesn't sense a flame, the unit's pilot light remains unlit, and the gas valve closes.
The flame sensor can become corroded due to carbon buildup from the flame. This can cause the sensor to fail. If the burner light goes out within seconds of switching on the unit, this is a telltale sign of a dirty sensor. If you see soot clearly covering the sensor, then it's time for a cleaning.
If you suspect the flame sensor is dirty or malfunctioning, cleaning it might help restore proper function. However, if you're unsure or uncomfortable performing maintenance yourself, it's a good idea to call a professional HVAC technician for a thorough inspection and service.
Notably, the flame sensors are dedicated to detecting the wavelength of flames, while the temperature sensor monitors the flame's temperature. In combination, the flame and temperature sensor identifies fires through the simultaneous analysis of flame wavelength and temperature.
1. Will a furnace run without a flame sensor? No, a furnace will not operate without a flame sensor.
Most furnace flame sensors cost less than $20, but if you opt to have a professional HVAC technician make the repair, you can expect to pay between $75 and $250. Need help replacing your flame sensor?
Flame sensors have an average lifespan of about five years. Therefore, you can expect to need to replace it at least twice before replacing your entire heating system.
Defective Igniter or Pilot Light
If it clicks but your furnace won't ignite after the combustion cycle, the electronic ignition systems probably need to be replaced. In cases where the furnace ignition starts normally but only stays on for a few minutes and then goes out, a new pilot light likely needs to be installed.
While the average life span of a flame sensor is about five years, many technicians recommend replacing the flame sensor a little more often at every two to three years. This schedule helps ensure that the flame sensor is always in good condition and not causing problems with the gas supply.
Flame sensors and thermocouples are both furnace safety components that sense heat and prevent gas leaks. However, the two parts function differently and are not interchangeable. Thermocouples are used in furnaces with pilot lights; flame sensors are used in furnaces with electronic ignitions.
Pilot Lights and Flame Sensors Could Be the Issue
A modern furnace without a pilot light relies on flame detectors to ensure the successful completion of a heating cycle. If the flame detector is covered in dust, dirt, or grime, you will quickly lose heat and your gas furnace will start blowing cold air.
Now that you know you can't bypass a flame sensor and need to buy a new one, shop around PlumbersStock for the right replacement flame sensor. We offer the best pricing on furnace parts, including furnace ignitors, motors, blower wheels, etc.
For instance, the flame sensor is on the left side, while the ignitor is located on the right side of the burners. When the burners produce a flame, the rod-shaped protrusion detects it and sends an electrical signal to the furnace's control board, signifying that everything is functioning correctly.
Flame detectors are also effective in detecting fires in areas where smoke detectors would be prone to false alarms, such as kitchens, garages, and other areas with high levels of smoke or steam. Flame detectors are also less prone to false alarms than smoke detectors.
If your furnace keeps turning off and on, your thermostat may be the culprit. A malfunctioning or improperly placed thermostat can cause your furnace to short cycle. Common issues include: Old wiring or dead batteries: Replace batteries or old wiring to ensure accurate temperature readings.
Flame sensors use two types of technology to identify flames: ultraviolet (UV) and infrared (IR). Depending on the installation, these sensor's reactions to a detected flame can include turning on a fire control system, sounding an alarm, and cutting a fuel line.