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My Furnace Won’t Turn On — What Went Wrong?

The winter wind's whipping up, so you set your thermostat, and...nothing. It's bitter cold outside, and your furnace won't turn on. Don't just throw up your hands in despair, you can take a closer look at what’s happening with your furnace.

Issues Preventing Your Furnace from Coming On

Potential Issues

  • not reaching temperature set on thermostat
  • no heat coming from vents
  • heating unit won't turn on

Inside your home's heating and cooling system, there is a blower motor that spins the fans to circulate air and keep the temperature even throughout your home. If debris gets into the fan or the bearings wear down, the motor can break down. When the blower motor fails, that circulation stops and your cooling or heating system will not work properly. But, before either system shuts down, the first thing you'll likely notice is that your home won't reach the temperature set on your thermostat. To get your systems back in line, you'll need to repair or replace your blower motor.

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  • furnace is blowing cold air
  • heating unit won't turn on
  • no heat coming from vents

The pilot light is the internal flame that keeps the heart of your furnace running. Each time your thermostat tells the furnace to turn on the heat, it uses the small, ever-burning pilot light to relight the burners. If it goes out for any reason, then the burners won't be able to light and your furnace won't be able to produce heat. In most cases, the pilot light can simply be relit. If it won't relight, there may be more significant issues with your furnace.

  • emergency heat light is on
  • HVAC unit is shut off
  • heating unit won't turn on
  • air conditioner won’t turn on

The control board is crucial for your comfort at home. The board (or panel) has a lot of responsibility, including turning your system on and off, processing system commands, and letting you know when there's an issue. If the control board fails, your entire HVAC system will shut down because the entire system relies on it. A malfunction in the control panel could be a result of faulty wiring, a loss of electrical power to the system, or a burnout of the control board itself. If your HVAC system is not working properly (you notice things like poor airflow or inconsistent temperatures), check the control board. When it malfunctions, you’ll see the panel light up with LED lights, or you might find burnt spots on the board. These are signs that it’s time for a decision to repair or replace the equipment.

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  • heating unit won't turn on
  • no heat coming from vents

Your gas furnace has an ignitor. Gas flows over the ignitor to create a flame within the heat exchanger. Air warms up as it passes over the flame. So without the ignitor, your furnace cannot produce warm air.

  • no power in some rooms
  • air conditioner won’t turn on
  • no power to devices
  • heating unit won't turn on
  • power is out
  • no heat coming from vents
  • thermostat is blank

A circuit breaker is the central source of electrical power in your home that supplies your network of electrical control circuits that run power to outlets, lights, alarms, etc with power. When your circuit breaker is overloaded with too much power for one reason or another, it trips. A tripped circuit breaker may cause you to lose power in one room or more, depending on how many rooms are powered by a circuit. It’s important to remember that tripped circuit breakers or blown fuses are not a cause, they are a symptom. Something else is going on with your system to cause it to overload.

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  • no power in some rooms
  • power is out
  • air conditioner won’t turn on
  • heating unit won't turn on

There are many individual circuits in a home. Power reaches breakers via the street transformer (or the electric service drop), which is the bundle of electrical cables that run from the utility company's power pole to the connection at your house. If the service drop goes down (or electrical service fails), all power in your home will shut off won't work properly.

  • thermostat is blank
  • no heat coming from vents
  • heating unit won't turn on

If your furnace isn't working, the issue could be as simple as a flipped power switch or emergency switch. A furnace switch can also be referred to as a furnace disconnect switch, which describes exactly what it does: disconnects furnace power to turn it on and off when needed. This switch often gets turned off accidentally, in situations such as by a contractor who was performing service, children playing around the furnace, or otherwise.

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