If your furnace clicks when the thermostat calls for heat but never actually starts, the system may be attempting to begin its normal startup sequence and failing somewhere along the way. The clicking sound may come from the thermostat, control board, gas valve, igniter or another electrical component. What happens immediately before and after the click can help narrow down the cause.
The thermostat may be sending the call for heat
Sometimes the first click you hear is simply the thermostat telling the furnace to start. If the thermostat clicks but nothing happens at the furnace, the problem may involve:
Thermostat wiring
A weak thermostat battery
A tripped breaker
A furnace power switch
A blown fuse
A control-board problem
Start by confirming that the thermostat is set to HEAT and that the temperature setting is above the current room temperature.
The furnace may have power but fail to start
A furnace can have electrical power and still fail during startup. You may hear a relay or control board click when the furnace receives the call for heat, but another component may prevent the sequence from continuing. If the furnace cabinet has a diagnostic light, check whether it is flashing a fault code. That code may help identify which safety control or component is preventing startup.
The igniter may be failing
Modern gas furnaces commonly use an electronic igniter. If the igniter is cracked, worn or electrically open, the furnace may begin the startup sequence but never light the burners. You may hear clicking as the system tries to start, followed by silence or another attempt a short time later. A hot surface igniter does not usually make a loud clicking sound itself, but the controls that energize it may.
The gas valve may be clicking without burner ignition
The gas valve can make an audible click when it opens.
If you hear that click but the burners do not ignite, the problem could involve:
The igniter
The gas valve
The gas supply
Dirty burners
Low gas pressure
Another ignition-control problem
If you smell gas, leave the area and contact the gas utility or emergency service from a safe location.
The inducer motor may not be starting
Many gas furnaces begin the heating cycle by starting the inducer motor. The inducer helps move combustion gases through the venting system. If the inducer motor does not start, the furnace may never get far enough in the sequence to ignite the burners. You may hear a relay click from the control board, but then nothing else happens. A failed inducer motor, blocked vent, electrical problem or control issue can all cause this symptom.
A pressure switch problem can stop the startup sequence
The pressure switch helps confirm that the furnace is venting properly. If the switch does not close when expected, the furnace may stop the ignition sequence before the burners ever light.
Possible causes include:
A blocked intake or exhaust pipe
A weak inducer motor
Damaged pressure tubing
A clogged condensate drain
A faulty pressure switch
Other venting problems
In this situation, you may hear clicking or repeated startup attempts without actual ignition.
A dirty or failing flame sensor is less likely if the burners never light
A dirty flame sensor usually causes the burners to ignite and then shut off a few seconds later. If your furnace only clicks and the burners never light at all, the problem is more likely to be earlier in the startup sequence. That may include the inducer motor, pressure switch, igniter, gas valve, gas supply or furnace controls.
The control board could be involved
The furnace control board manages the startup sequence and sends power to the various components in the correct order. A relay on the board may click even if the board is not successfully powering the next component. Control boards can fail, but they should not be replaced based on clicking alone. A technician can test the board output and determine whether the problem is actually the control board or another component that is preventing startup.
A tripped safety switch may keep the furnace from running
Gas furnaces contain several safety switches.
Depending on the furnace, these may monitor:
Venting
Flame
Furnace temperature
Blower-door position
Condensate drainage
If one of these switches is open, the furnace may refuse to continue the startup sequence. The clicking you hear may simply be the control board attempting to initiate a cycle.
Could the problem be something simple?
Yes.
Before calling for service, you can safely check a few basic things:
Make sure the thermostat is set to HEAT
Raise the thermostat setting a few degrees
Replace weak thermostat batteries
Check the furnace circuit breaker
Make sure the furnace power switch is on
Check that the furnace access panel is fully closed
Inspect the furnace filter
If the furnace still clicks but will not start, the problem likely needs further diagnosis.
Why does my furnace click repeatedly?
Repeated clicking usually means the system is trying to complete the startup sequence more than once. The furnace may start an ignition attempt, detect that something is wrong, stop, and then try again. After several failed attempts, the furnace may go into lockout. Repeated clicking is especially important to investigate if the furnace never produces heat.
When should you call for furnace repair?
You should have the furnace inspected if:
It clicks but never starts
The inducer motor does not run
The igniter does not glow
The burners never light
The furnace repeatedly attempts startup
The furnace goes into lockout
The diagnostic light shows a recurring fault code
You smell gas or burning
The problem keeps returning after a reset
A technician can follow the furnace startup sequence step by step and identify exactly where it is failing.
Need help with a furnace that clicks but will not start?
If your furnace clicks but does not turn on, the problem could involve the thermostat, inducer motor, pressure switch, igniter, gas valve, control board or another safety component.
Roberts Brothers Comfort can diagnose the startup sequence, find out why the furnace is not turning on and make the necessary repairs. We provide expert furnace repair service throughout Ohio’s Miami Valley region including Casstown, Covington, Fletcher, Piqua, Rosewood, Saint Paris, Sidney, Tipp City, Troy, Urbana, West Milton and all the surrounding areas.
