​Why Won't My Furnace Turn On? | Air Experts

Nobody wants to deal with a furnace that won’t turn on when it’s cold outside. 

If you’re having issues with your furnace turning on, don’t worry. We’re here to help you quickly troubleshoot the problem.

In this blog, we’ll go over the following DIY repairs you can try at home before you call a professional for help:

  • Checking thermostat settings
  • Resetting a tripped circuit breaker
  • Replacing a dirty air filter

We’ll also go over possible issues that will require the help of an HVAC pro.

Want a professional to check your furnace ASAP? Our trusted technicians are standing by, ready help. Call (732) 681-9090 or schedule an appointment online today.

DIY solution #1: Check your thermostat settings

The first thing you need to do is check to make sure your thermostat is powered on and set to the right settings. 

  1. First, check to make sure your thermostat has power and is responsive. If the display is off or the thermostat is unresponsive, try changing the batteries to see if that fixes the problem.
  2. Verify that the thermostat is set to HEAT. This may seem obvious, but it’s always good to check in case the setting was unintentionally switched to COOL or OFF.
  3. Set the temperature to a high setting and make sure it is on RUN mode instead of HOLD or STANDBY. 

If you’ve followed the steps above and your furnace still won’t turn on, we recommend calling a professional. They’ll do a thorough inspection of your thermostat and its wiring and will be able to diagnose the problem.

DIY solution #2: Reset a tripped breaker

Sometimes a power outage, power surge or an overworking furnace can trip the circuit breaker (located in the electrical panel) to prevent electrical currents from causing damage to your furnace. If the circuit breaker is tripped, your furnace won’t start.

To see if this is the issue, go to your electrical panel and check to see if the furnace breaker is flipped to the OFF position. If it is, you can try to reset it to see if your furnace will turn on. 

If the breaker continues to trip, do not keep resetting it. Instead, call a professional. If you keep resetting your breaker, you risk damaging your furnace and your home. 

DIY solution #3: Change your air filter

If your furnace is overheating, it will shut itself off to prevent damage. Overheating could be the reason your furnace won’t turn on.

There are a few things that can cause a furnace to overheat, but one of the most common is a dirty or clogged air filter. 

Check to see if your air filter is dirty. A dirty air filter should be replaced immediately to prevent further overheating. If you replace the air filter and your furnace still doesn’t start and run smoothly, contact an HVAC pro ASAP. 

Other issues that require a professional

If you’ve gone through all of the DIY steps listed above and are still having trouble, chances are you’ll need to contact a professional for help.

Here a some common reasons your furnace won’t turn on that will require the help of a professional: 

Problem #1: Overflowing condensate drain or pump

High-efficiency furnaces produce condensate which is drained or pumped outside so it’s not leaking inside of your home. 

If there is a clog (or another issue with the condensate drain or pump), the condensate can overflow, triggering the float switch and shutting off the furnace. The float switch is a safety device that shuts off the furnace when it detects liquid that’s overflowing into the drain pan. If this is the case, this could explain why your furnace won’t turn on.  

Problem #2: Electrical ignition problem

Most new furnaces have an electrical ignition system that starts the heating process. If the ignition system is broken, the furnace won’t be able to heat your home. This is something that an HVAC professional can troubleshoot for you. They’ll inspect your furnace and the ignition system to determine what’s causing the problem. 

Problem #3: Fuel leak or issue

Another possibility is a fuel leak or a lack of fuel supply to your system. If your system detects a leak or if it isn’t receiving fuel for whatever reason, then it won’t start.

If this is the case, your furnace is designed to shut itself off to protect you from exposure to harmful gases.

When you contact a professional, they’ll check the gas valves and burners to make sure your furnace is getting fuel. They’ll also check to see if the part that detects leaks in your furnace (known as the  flue gas spill switch) has triggered. If it has, a technician can reset it and find the source of the gas leak in your system. 

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