A thermocouple is a flame sensor that, when it detects a pilot flame, opens gas valves to the furnace burners. However, if the thermocouple is malfunctioning or covered in soot, it won't sense the pilot flame and shut the gas valve. The spark igniter will spark (click) for about a minute trying to ignite the flame.
While moisture and rust are one of the most common causes of delayed ignition in furnaces, dust and lint can also accumulate and cause problems. This can be easily remedied by having your furnace inspected and cleaned by professionals before each heating season.
The common sources of a furnace clicking sound are:
If it's faulty or dirty, it won't send the signal and the ignitor will click. Ignitor flame — The flame itself can run too cold to burn the gas or oil effectively, so the ignition clicks for several minutes or unendingly.
The top causes to blame when a furnace kicks on and off are: The air filter needs changed. The thermostat batteries need to be replaced. Blower motor malfunctions.
You can reset the ignition on your furnace simply. To do this you must cut the power to the furnace first by turning off the circuit that powers it. Once the power is off you can remove the burner door to reveal the ignitor. Turn this to “off” and leave it off for at least 5 minutes.
If your furnace's air filter is clogged or dirty, it can reduce the amount of air flowing through the system. This lack of airflow will cause your furnace blower to work harder and cycle on and off more often than usual.
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
Check for food debris and blockage
Food remnants and debris can obstruct the igniter from sparking, which could lead to a clicking noise without ignition. Ensure that the area around the igniter is clean and dry before trying again.
1. The Furnace Won't Run. When a furnace doesn't run at all, that could be a sign you have a bad ignitor that needs replacing.
A good cleaning and calibration should resolve the problem. Bearings keep the blower running smoothly. Just like any other furnace component, however, they can wear out. Dirt, dust, and debris may block the bearings, and when this happens, odd noises are common.
A worn-out igniter can periodically fail, and if it keeps trying to light the gas, your furnace will make a clicking sound. The noise may last until the flame ignites or the gas valve closes.
The simple solution: Turn your furnace off and check the filter. If it's dirty or it's been 3 months or more since you changed it, put a new, high-quality filter in place.
If your furnace shuts off after a few minutes and starts more than eight times an hour, it may require repair. Common causes of furnace short cycling include restricted airflow, a malfunctioning flame sensor, or a poorly placed thermostat.
Most modern gas furnaces can be reset by turning off the power, waiting around 20 seconds, then switching the power back on. Other furnace models may exit lockout after 1-2 hours and attempt to power on again.
Remove the ignitor carefully by holding only the base. Avoid touching the ignitor surface with bare hands. Use compressed air to remove carbon deposits. Gently wipe the surface with a soft cloth or scuff pad until shiny.
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. This is a frustrating problem, but an HVAC technician can fix it.
Most furnaces kick on and off between three to eight times an hour, depending on things like outdoor air temperatures, the furnace's age, and how much insulation you have. That's why, instead of asking how often a furnace should cycle, it's best to stay alert to changes in how your furnace is running.
Dirty Air Filters
So, the furnace is triggered to stop, then it cools down only to fire back up again. This short cycling continues to repeat until the furnace receives the airflow it needs. Dirty air filters are one of the most common reasons behind furnace short cycling.
If it's broken or malfunctioning, it may fail to detect the flame and shut off the gas supply as a precaution, even if the burners are actually lit. This can result in your furnace starting the ignition process but failing to stay lit.
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.