Furnace That Won’t Turn On with the Thermostat

As the chilly days of winter approach, a functioning furnace becomes essential to keep your home warm and comfortable. However, it can be incredibly frustrating when you set your thermostat to the desired temperature, only to find that your furnace refuses to turn on. Before you panic and call a technician, there are several steps you can take to troubleshoot the issue yourself. In this blog post, we’ll guide you through the common reasons why your furnace won’t turn on with the thermostat and provide solutions to help you get your heating system back in action.

Check the Thermostat


A tripped circuit breaker is a common cause of furnace problems. Head to your electrical panel and check if the circuit breaker that controls your furnace is in the “on” position. If it’s tripped, reset it and try turning on the furnace again. If the breaker trips again, it’s best to consult a professional electrician, as this indicates an electrical issue.

Replace the Air Filter

A clogged or dirty air filter can obstruct airflow, causing your furnace to overheat and shut down as a safety measure. Regularly changing or cleaning your furnace’s air filter is essential for its proper functioning. Refer to your furnace’s manual to locate and replace the air filter, which is usually found near the blower motor.

Check the Furnace Switch

Furnaces typically have a power switch located near the unit itself. Ensure that this switch is in the “on” position. Over time, it’s possible for this switch to be accidentally turned off, leading to a non-functioning furnace.

Inspect the Pilot Light (for Gas Furnaces)

If you have a gas furnace, check if the pilot light is lit. If it’s not, you may need to relight it following the manufacturer’s instructions. A malfunctioning pilot light can prevent your furnace from turning on. If the pilot light keeps going out, it could be a sign of a more significant issue, and you should contact a professional technician.

Reset the Furnace

Modern furnaces often have a reset button or switch. If your furnace has one, try resetting it by turning it off and then on again after waiting for a few minutes. This can sometimes resolve minor issues with the furnace’s control system.

Call a Professional

If you’ve gone through the above steps and your furnace still won’t turn on with the thermostat, it’s time to contact a professional HVAC technician. They have the knowledge, experience, and tools to diagnose and repair more complex furnace problems. Attempting to fix a furnace issue beyond your expertise can be dangerous and may lead to further damage or safety hazards.

Certainly, let’s continue with some additional information and tips to keep in mind:

Preventative Maintenance:

Prevention is often the best way to avoid furnace issues in the first place. Consider scheduling annual or bi-annual maintenance check-ups with a qualified HVAC technician. These professionals can inspect and service your furnace to catch potential problems before they become major issues.

Invest in a Smart Thermostat:

Modern smart thermostats offer advanced features and remote control capabilities. They can provide you with insights into your heating system’s performance and alert you to any potential problems. Some even have self-diagnostic features that can detect issues and notify you or your HVAC technician.

Keep the Area Around Your Furnace Clear:

Make sure the area around your furnace is clear of obstructions. Boxes, clutter, or debris can block airflow or access to the furnace components, making it difficult to troubleshoot or service the unit.

Learn About Your Furnace:

Take some time to familiarize yourself with your furnace’s user manual. It contains valuable information about troubleshooting, maintenance, and safety precautions specific to your unit. Knowing the basics can help you address minor issues more effectively.

Safety First:

If you ever smell gas or suspect a gas leak, immediately turn off the gas supply to your furnace, open windows to ventilate the area, and leave your home. Call your gas company and a professional technician to address the issue. Gas leaks can be extremely dangerous.

Consider a Carbon Monoxide Detector:

Carbon monoxide (CO) is a colorless, odorless gas that can be produced by a malfunctioning furnace. To ensure your safety, install carbon monoxide detectors in your home, especially near bedrooms and areas adjacent to your furnace.

Certainly, let’s explore a few more advanced troubleshooting steps and considerations for addressing a furnace that refuses to turn on:

Inspect the Ignition System (for Gas Furnaces):

If you have a gas furnace with an electronic ignition, it’s possible that the ignition system is faulty. Modern gas furnaces typically use either a hot surface ignition or intermittent pilot ignition. If you’re comfortable doing so and have experience working with gas appliances, you can carefully inspect these components for signs of damage or malfunction. However, if you’re unsure, it’s safer to leave this task to a professional technician.

Check the Thermostat Wiring:

Sometimes, thermostat wiring issues can prevent your furnace from turning on. Inspect the thermostat wiring to ensure there are no loose or damaged wires. If you suspect a wiring problem, consider calling a technician to properly diagnose and fix it.

Examine the Limit Switch:

The limit switch in your furnace plays a crucial role in regulating the blower fan. If the limit switch is faulty or stuck, it may cause your furnace to shut down prematurely. Consult your furnace’s manual to locate the limit switch and check if it’s functioning correctly. If you’re uncertain about this step, it’s best to consult a professional.

Consider a Furnace Replacement:

If your furnace is old, inefficient, or has experienced frequent breakdowns, it might be time to consider replacing it with a newer, more energy-efficient model. A professional HVAC technician can assess your current system’s condition and recommend the best replacement options based on your heating needs and budget.

Regular Maintenance Is Key:

Even if you manage to resolve the immediate issue causing your furnace not to turn on, remember that regular maintenance is crucial for the long-term health of your heating system. Annual maintenance checks can identify and address potential problems before they become major disruptions.

Emergency Heating Alternatives:

While you work on resolving the issue with your furnace, it’s important to have alternative heating sources available, especially if you live in a cold climate. Portable space heaters, electric blankets, or staying with friends or family can help you stay warm until your furnace is back in operation.

Possible Thermostat Issues

IssueDescriptionSolutionTools NeededDifficulty Level
Thermostat Not SetThermostat set to the wrong temperatureAdjust the thermostat settingsNoneEasy
Dead BatteriesThermostat batteries are deadReplace thermostat batteriesScrewdriverModerate
Loose WiringWiring connections are looseTighten loose wiresScrewdriverModerate
Incorrect ModeThermostat set to the wrong modeSwitch to the correct modeNoneEasy
Thermostat FaultThermostat malfunctioningReplace the thermostatScrewdriverDifficult

Furnace Power Issues

IssueDescriptionSolutionTools NeededDifficulty Level
Power Supply IssueFurnace not receiving powerCheck power supply connectionsMultimeterModerate
Circuit BreakerCircuit breaker trippedReset the circuit breakerNoneEasy
Fuse BlownFurnace fuse blownReplace the blown fuseScrewdriverModerate
Pilot Light OutPilot light is not litRelight the pilot lightLighterModerate
Faulty IgnitionIgnition system malfunctionCall a technician for repairNoneDifficult

Air Filter Issues

IssueDescriptionSolutionTools NeededDifficulty Level
Clogged Air FilterAir filter is dirty or cloggedReplace or clean the air filterNoneEasy
Wrong Filter SizeIncorrect filter size installedReplace with the correct sizeNoneEasy
Filter OrientationAir filter installed incorrectlyInstall the filter correctlyNoneEasy
Restricted AirflowReduced airflow due to a clogged filterClean or replace the air filterNoneModerate
No Air FilterNo air filter installedInstall an appropriate air filterNoneEasy

Sensor and Wiring Issues

IssueDescriptionSolutionTools NeededDifficulty Level
Sensor MalfunctionTemperature sensor malfunctionReplace the faulty temperature sensorScrewdriverModerate
Damaged WiringDamaged or frayed wiringRepair or replace damaged wiringWire strippers, electrical tapeModerate
Short CircuitElectrical short circuitIdentify and fix the short circuitMultimeter, soldering ironDifficult
Thermostat WiringThermostat wiring issuesReconfigure or replace thermostat wiringScrewdriverModerate
Control Board IssueFurnace control board malfunctionReplace the control boardScrewdriverDifficult

Miscellaneous Issues

IssueDescriptionSolutionTools NeededDifficulty Level
Gas Supply IssueNo gas supply to the furnaceCheck and restore gas supplyGas shutoff valveModerate
Blocked VentsBlocked or obstructed furnace ventsClear obstructions from the ventsNoneEasy
Ductwork IssuesDuctwork problems affecting airflowInspect and repair ductwork issuesDuct tape, screwdriverModerate
Safety Switch TrippedFurnace safety switch trippedReset the safety switchNoneEasy
Excessive Dirt/DebrisAccumulated dirt or debris in the furnaceClean the furnace interiorVacuum cleaner, brushesModerate


In conclusion, addressing a furnace that won’t turn on with the thermostat can involve a range of troubleshooting steps, from simple checks to more complex diagnostics. If you’re ever uncertain about your ability to safely troubleshoot or repair your furnace, it’s wise to consult a professional HVAC technician. Investing in regular maintenance and considering energy-efficient replacements when necessary can help ensure your home remains comfortable and warm during the winter months.

Furnace That Won't Turn On with the Thermostat

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