Thermostat clicks but furnace doesn’t turn on.

Thermostat clicks but furnace doesn’t turn on [Solved].

You might notice that you get no heat or air, even though your thermostat clicks as it calls for heat.  This clicking is a relay inside that closes to switch on the furnace.

Now this no heat or air situation can happen for many reasons.

Incorrect wiring, tripped circuit breakers, blown fuses, loss of gas supply, burned out heating elements, or a broken HVAC system could cause this.

Here, we describe some of these causes, and then offer troubleshooting procedures and repair hints to resolve them.

Also read>>>>Honeywell Thermostat connection failure.

Why Thermostat Clicks but Furnace Doesn’t Turn On:


  • The thermostat Was Incorrectly Wired.
  • There is faulty wiring between the thermostat and furnace.
  • Defective thermostat.
  • Loss of power / gas to furnace heaters or compressors.
  • Dirty or defective ignitor or pilot light.
  • Defective control board in furnace.

Detailed Explanation:

1.The thermostat Was Incorrectly Wired.


If you find yourself in a predicament where the thermostat clicks but the furnace doesn’t turn on, especially following the installation of a new thermostat, it’s highly plausible that a wiring mishap is to blame.

One common error is the accidental reversal of the W and Y wires, inadvertently causing the cooling stage to activate despite the thermostat’s call for heat.

Such a mix-up can trigger a cascade of symptoms, contingent upon the wires affected and their connection points on the thermostat.


To remedy this perplexing situation, commence by meticulously inspecting the wiring at both the thermostat and furnace terminations.

At the thermostat, ensure that all wires are correctly affixed to their designated terminals on the wall plate.

Subsequently, replicate this process at the furnace terminus.

If the prospect of aligning these wires with the appropriate terminals fills you with uncertainty, don’t hesitate to solicit the assistance of a seasoned heating system repair specialist.

They possess the expertise to decipher the intricacies of thermostat configurations and rectify any misalignments, ultimately alleviating the conundrum of “thermostat clicks but furnace doesn’t turn on” that you may be facing.

Also read>>>>HoneyWell Thermostat Blank Screen.

2.There is faulty wiring between the thermostat and furnace.


A recurrent problem that can lead to the frustrating scenario of “thermostat clicks but furnace doesn’t turn on” arises when the solid copper wires within the thermostat cable endure excessive flexing.

These wires are susceptible to breakage, whether due to frequent bending or, in some cases, if the cable was inadequately secured using excessive stapling pressure or misaligned stapling techniques, resulting in cable nicks.

The manifestation of this issue is typically detected during initial thermostat testing, but it can also remain dormant for years, lurking beneath the surface.

Over time, the settling of wall studs can induce wire flexing, causing gradual wear on the wire coverings, ultimately disrupting the heat operation.

In such instances, the thermostat maintains its power supply from the furnace, but the wires responsible for conveying heat requests become damaged or severed.

Consequently, the thermostat, though functional itself, becomes incapable of communicating its heat requirements to the furnace.


To resolve this predicament effectively, it is imperative to replace the cable connecting the thermostat to the furnace.

When securing the cable, exercise caution not to tightly staple it, and avoid using excessive fastening force. Instead, opt for a more relaxed, loose placement that minimizes the risk of wire damage.

This proactive approach ensures that the issue of “thermostat clicks but furnace doesn’t turn on” is eradicated, facilitating seamless communication between the thermostat and the furnace for uninterrupted heating performance.

Also read>>>Thermostat Keeps Clicking.

4.Defective thermostat.


In cases where the control relay within the thermostat audibly clicks to signal the need for additional heat, it’s possible that the relay itself has succumbed to wear and tear.

Over time, the relay’s internal contacts may deteriorate, resulting in an insufficient connection when they attempt to close together.

This decline in contact quality can lead to the persistent problem of “thermostat clicks but furnace doesn’t turn on.”


Your most reliable course of action in this situation is to acquire a new thermostat.

Replacing the worn-out thermostat with a fresh one ensures the restoration of optimal functionality without the hassle of delving into intricate repairs.

Alternatively, if you’re inclined to explore a DIY approach and have a known-good thermostat readily available, consider swapping it in place of your existing one.

By doing so, you can discern whether the original thermostat is indeed the culprit behind the “thermostat clicks but furnace doesn’t turn on” predicament.

This method serves as a practical means of troubleshooting and may uncover the source of the issue, saving you both time and resources in the process.

Also read>>>>Thermostat Says Heat On But No Heat.

5.Loss of power / gas to furnace heaters or compressors.


Though the furnace turns on, you may notice that the heating elements such as burners, electric coils, or heat pump compressors do not come on as well. 

This can happen due to a loss of electric power to said elements due to tripped circuit breakers, failed heating elements, broken relays, or a faulty control board. 

Or in the case of gas furnaces, it could be a loss of gas supply or faulty ignitor (the device that lights the gas coming out of the burner when the t-stat calls for heat, and again, faulty wiring or broken control board.


  • Check circuit breakers. Make sure all breakers that feed the furnace and any outdoor components are ON.  For gas heating, assure that your gas supply is okay by checking that your other gas appliances are still working and that no one has mistakenly closed the gas valve that feeds the furnace.  Also, are you up to date on your gas bill? If breakers keep tripping, then seek help from a qualified electrician or HVAC technician.
  • Check connections in furnace. Most furnaces have at least a couple cables that plug into other cables, to control boards, or relays.  So make sure that these are all tight and properly seated, because one loose connection can prevent heat from activating.
  • Make sure gas burners are clean.  It’s a useful maintenance practice to clean the burner jets yearly, as some being clogged can cause protective circuits to prevent the gas valve that feeds the burner from opening.

Also read>>>>Honeywell Thermostat Aux Heat.

6.Dirty or defective ignitor or pilot light.


When you hear the reassuring click of your thermostat signaling the heat to activate, it should ideally prompt the ignitor, whether it’s of the spark type or the hot metal variety, to engage simultaneously with the release of gas (in the case of gas furnaces).

However, over time, these critical components can experience burnout.

Additionally, if your furnace relies on a pilot light, a diminutive flame supplied by the gas feed, positioned near the primary burner, serves as the ignition source when heat is required.

Should this flame extinguish due to dirt accumulation or clogged piping, your thermostat’s call for warmth will go unanswered, resulting in the frustrating scenario of “thermostat clicks but furnace doesn’t turn on.”


To resolve this vexing issue, consider the following steps:

  • Clean the Pilot Light Jet: Turn off the gas supply to the pilot light and delicately clean the nozzle using a toothbrush. Removing dirt and debris from the nozzle can help restore the pilot light’s functionality.
  • Inspect and Replace the Pilot Light Sensor: This sensor is responsible for detecting the presence of a pilot flame before allowing gas to flow to the main burner. If the sensor is malfunctioning due to a lack of flame or damage, it will prevent the furnace from heating, despite the thermostat’s command.
  • Replace the Ignitor: If your furnace uses an ignitor, it may need replacement. Ensure that the new ignitor is correctly positioned, situated close enough to the main burner to effectively ignite the incoming gas when the thermostat triggers the heating cycle.

By addressing these potential issues, you can eliminate the frustrating problem of “thermostat clicks but furnace doesn’t turn on,” ensuring your heating system operates smoothly and efficiently.

7.Defective control board in furnace.


Saving the most challenging problem for last, we confront a situation where resolving the issue of “thermostat clicks but furnace doesn’t turn on” is likely to be the costliest endeavor.

Control boards, responsible for orchestrating the furnace’s entire operation, often come with a substantial price tag, not to mention potential labor expenses if you enlist the services of a professional technician.

Nevertheless, control boards can indeed malfunction on occasion. These vital processors, when compromised, render the furnace unresponsive to heat calls from the thermostat.


To address this formidable issue, consider the following steps:

  • Replace the Control Module: The most effective course of action is to replace the control module. However, this is a task best left to professionals, as the intricate process of removing the old module and installing the new one requires a level of expertise that exceeds the capabilities of amateur HVAC enthusiasts.
  • Diagnostic Precision: Before investing in a costly control board replacement, it is imperative to accurately diagnose the problem. Mistakenly identifying the control board as the culprit can be a costly error, as most parts supply centers do not accept returns or provide refunds for modules that have been purchased in error.

Given the complexity and expense associated with control board replacement, we strongly recommend seeking the expertise of experienced professionals when dealing with this issue of “thermostat clicks but furnace doesn’t turn on.”

Their knowledge and precision will ensure a correct diagnosis and a successful resolution to the problem, sparing you unnecessary expenses and frustration.

Also read>>>>Furnace Shuts Off After 30 Seconds.


In conclusion, troubleshooting the issue of “thermostat clicks but furnace doesn’t turn on” can be a complex endeavour with various potential causes and solutions.

This problem can arise from a range of issues, including thermostat miswiring, damaged wires, malfunctioning sensors, pilot light problems, and even control board failures.

To resolve this issue effectively, it’s essential to approach it methodically:

  • The thermostat Was Incorrectly Wired.
  • There is faulty wiring between the thermostat and furnace.
  • Defective thermostat.
  • Loss of power / gas to furnace heaters or compressors.
  • Dirty or defective ignitor or pilot light.
  • Defective control board in furnace.

Remember that safety should always be a top priority when dealing with heating systems. If you’re uncertain about any step or if the problem persists, it’s advisable to seek the expertise of a qualified HVAC technician.

In many instances, the resolution of the “thermostat clicks but furnace doesn’t turn on” problem can be straightforward, but it may require some troubleshooting effort.

By carefully following the steps outlined and, if needed, seeking professional help, you can ensure your heating system operates smoothly, providing the warmth and comfort your home deserves during the chilly months.