Troubleshooting a Furnace That Will Not Turn On With Thermostat

A malfunctioning furnace can be a source of discomfort, especially during colder months. If your furnace refuses to turn on despite adjusting the thermostat, it’s essential to troubleshoot the issue systematically before calling in a professional. This step-by-step guide will help you identify common problems and potentially resolve them on your own.

1. **Check Thermostat Settings:**

Start by ensuring that your thermostat is set to the desired temperature. Sometimes, simple oversights in temperature settings can lead to a seemingly non-functional furnace. Set the thermostat a few degrees higher than the current room temperature and wait a few minutes to see if the furnace responds.

2. **Change Thermostat Batteries:**

Some thermostats are battery-powered. If the batteries are weak or dead, the thermostat may not communicate properly with the furnace. Replace the batteries and see if this resolves the issue.

3. **Inspect Circuit Breakers:**

Locate the circuit breaker for your furnace in the main electrical panel. Check if it’s tripped or in the off position. If so, reset it by turning it off and then back on. A tripped circuit breaker could be the reason why power isn’t reaching the furnace.

4. **Check Furnace Power Switch:**

Locate the power switch on or near your furnace. Ensure that it’s in the “on” position. If the switch is off, turn it on and wait a few minutes to see if the furnace starts running.

5. **Examine Air Filter:**

A clogged or dirty air filter can restrict airflow, causing the furnace to overheat and shut down. Check the air filter and replace it if it’s dirty. This is a simple yet crucial step in maintaining your furnace’s efficiency.

6. **Inspect Pilot Light (For Gas Furnaces):**

If you have a gas furnace, check the pilot light. If it’s out, relight it following the manufacturer’s instructions. If the pilot light won’t stay lit, there may be a deeper issue, and it’s advisable to seek professional assistance.

7. **Reset the Furnace:**

Some furnaces have a reset button. If your furnace has one, press it and wait for the furnace to restart. This may solve issues related to overheating or minor malfunctions.

8. **Thermostat Wiring:**

Inspect the thermostat wiring to ensure there are no loose or disconnected wires. If you’re comfortable doing so, you can tighten or reconnect any loose wires. If you’re uncertain, it’s best to consult a professional.

9. **Check for Error Codes:**

Modern furnaces often have diagnostic features that display error codes. Refer to your furnace’s manual to understand these codes and troubleshoot accordingly. If you can’t find a solution, it’s time to call a professional technician.

10. **Schedule Professional Maintenance:**

If all else fails or if you are uncomfortable performing any of the troubleshooting steps, it’s advisable to schedule a professional inspection and maintenance service. Certified technicians can identify and address more complex issues that may be beyond the scope of basic troubleshooting.


Troubleshooting a furnace that won’t turn on with the thermostat can often be resolved with a few simple steps. By following this guide, you can identify common issues and potentially fix the problem yourself. However, if you encounter difficulties or the problem persists, it’s crucial to seek the expertise of a professional HVAC technician to ensure the safe and efficient operation of your furnace.

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