Furnace
Help! My furnace won't turn on

Having a hard time getting your furnace to kick on? You might be able to fix the problem yourself.

Before you call a professional, try troubleshooting the common problems below:
  • Check the thermostat
  • Make sure your furnace has power
  • Empty the drain pan (on condensing furnaces only)

We’ll go into more detail about how to troubleshoot each of these problems. If these tips don’t get your furnace running again, you likely have a bigger problem that a professional will need to fix.

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Tip #1: Check the thermostat

The thermostat is the brain of your HVAC system. Your system won’t even turn on without the thermostat telling it to.

So, if your furnace isn’t kicking on when you want it to, the problem could be one of the common thermostat issues below:

  1. The thermostat is set to COOL. Someone could have accidentally switched the setting from HEAT.
  2. The thermostat is in HOLD/STANDBY mode. When in this mode, your thermostat will override the programmed temperature, allowing you to adjust the temperature as needed. You can use HOLD mode to test thermostat operation. If your furnace kicks on when you manually increase the temperature, everything should be working properly. To turn off HOLD mode, press the RUN button.
  3. The thermostat batteries are dead. If your thermostat isn’t getting power, it can’t tell your furnace when to turn on. Replacing the batteries should fix the problem.

Tip #2: Make sure your furnace has power

Even gas furnaces require electricity to start up. If your unit isn’t getting electricity, that could explain why it won’t turn on.

Your furnace can lose its electrical connection in 2 places:
  1. Circuit breaker: Located on your home’s main electrical panel, your furnace’s dedicated circuit breaker could have tripped, which would cut off electricity to your system. If the breaker switch is flipped to OFF or in the middle between ON and OFF, the breaker has tripped. Depending on your panel, you might have to flip the switch to OFF before flipping it back to ON. Note: The circuit breaker is designed to protect your furnace from power surges. If the breaker keeps tripping, you have a bigger electrical problem that a pro will need to fix.
  2. Disconnect switch: Usually mounted on the side of the furnace or a nearby wall, the furnace disconnect allows a plumber or tech to disconnect electricity to the furnace without having to switch off the circuit breaker. Flipping the switch back to ON should make your furnace kick back on.

    3. Tip #3: Empty the drain pan

    If you have a high-efficiency (90+ AFUE) furnace, also called a condensing furnace, it creates condensation. This moisture drains into a pan beneath your air handler that carries it down a condensate line.

    Some condensing furnaces will have a condensate pan overflow switch, also called a “float switch”, that’s designed to shut off power to the furnace if your drain line gets clogged and the pan overflows.

    If your furnace has a float switch, you can check if an overflowing drain pan is the issue by following the steps below:
    1. Locate your air handler, which is normally in an attic, basement or closet.
    2. Check the drain pan (a metal tray) that sits below the air handler.
    3. Remove any standing water. The float switch will settle back to the bottom of the pan and should automatically restore power to the furnace.
    4. If the switch doesn’t reset after trying the steps above or your drain pan keeps overflowing, you’ll want to call a professional.

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