Furnace Stopped Working: DIY Fixes

Furnace
Comstock Images/Stockbyte/Getty Images

On those cold days, we depend on our furnaces to keep the house toasty and warm. So, it is never fun to wake up in the morning or to come home, only to discover interior temperatures hovering barely above exterior temperatures. Clearly, your furnace has stopped working and things are getting serious.

Before you panic and immediately call in an HVAC technician, there are a few things you can try to fix your furnace by yourself. True, furnaces are complex, and more complicated repairs are usually best left in the hands of licensed technicians. But before calling in the technicians, there are a few DIY fixes to first try if your furnace has stopped working—power, thermostat, and condensate and pan.

Fix Power Problems

When your bathroom fan, kitchen microwave, or dining room light fail to operate, your natural instinct might be to check the switch or to see if the circuit breaker has tripped off. In some cases, fixing your furnace is as simple as flipping a circuit breaker back on.

  1. Locate your electric service panel and open the door.
  2. Find the circuit breaker that controls the furnace. Furnace usually have two circuit breakers, not one. They should be next to each other, top and bottom. Or the circuit breakers may be in the form of one large breaker the size of two smaller breakers.
  3. Flip the circuit breaker backward, toward the outside. Then, flip it inward. It should snap into place, activating the furnace.

Another way to see if your furnace is receiving power involves the toggle switch on the side that allows you to manually turn on fan-only operations. Flipping this switch and listening for the fan allows you to double-check that the furnace is receiving power. Even if the burner part of the furnace is not operable, other parts of the furnace are working.

Do Gas Furnaces Work Without Electricity?

Both gas and electric furnaces require electricity in order to work. For gas furnaces, even though gas is the fuel that provides the heat, electricity is needed to operate the blower motor, relays, circuit boards, and more. Gas furnaces, then, cannot operate without electricity.

Check the Thermostat

Checking the thermostat when the furnace stops working is one of those solutions that seems all too simple and obvious. Yet there may be a few aspects that you have not considered.

  1. Is the automatic clock on the programmable thermostat accurate? If the clock is off, then the schedule will not operate correctly.
  2. Do the batteries need changing? Many thermostats operate off of the low-power current from the wire that attaches to the thermostat, so they will have no batteries. But programmable thermostats usually do have on-board batteries that need to be changed out. If you find the programmable thermostat too difficult to understand, switch it out for an older style dial analog thermostat, if only for testing purposes.
  3. Carefully detach the thermostat from the wall. Ensure that the wire coming out of the wall is securely attached to the thermostat.
  4. Check the thermostat wire at the furnace to make sure that it is still connected.

Fix the Condensate Pump and Pan

If you have owned your furnace long enough, you may have wondered about a faint buzzing that your furnace frequently emits, a sound similar to that of a water pump for an aquarium or water feature. You may have heard this sound after a long heating cycle. The sound runs for a few minutes, then it stops.

This is the condensate pump and the sound is normal. After heat cycles, water condensation is drawn from the air and deposited into the furnace. This condensation builds up so much that it has no time to evaporate back into the air.

Where Is the Furnace Condensate Pump?

The condensate pump and pan is a unified device about the size of a shoebox. It is located on the side of the furnace. Sometimes, it will be powered by an auxiliary outlet next to the furnace. Other times, it is hard-wired into the furnace and is powered directly by the furnace.

Unlike a window unit air-conditioner, which is located on the home's exterior and can deposit the water onto the ground, furnaces are usually centrally located within a home. This leaves no place for the water to exit on its own. The condensate pan collects the water and its attached condensate pump expels it out of the house.

  1. Turn off all circuit breakers controlling the furnace. If the condensate pump is powered by an auxiliary outlet, then you will need to turn off the circuit breaker for that outlet, too.
  2. Look for the rectangular-shaped box attached to the side of the furnace. Do not remove it.
  3. The pump may be plugged into a GFCI outlet nearby. The GFCI may have flipped off, cutting off power to the condensate pump. Reset the GFCI outlet. If the GFCI will not reset, replace it.
  4. Check the tube that runs from the condensate pump to the outside and make sure that it is not pinched or blocked.
  5. Open the lid to the condensate pan (usually removing the condensate pump in the process). Check to see if the draw tube is still at the bottom.
  6. The condensate pump pan might be overly full and leaking on the floor. If so, the automatic switch on the pump that triggers when the water level rises is not working. Manually flip the switch back and forth a few times to loosen it.
  7. If the condensate pump is not working, replace it entirely. Condensate pumps are relatively inexpensive and easy to replace. If the pump is hard-wired into the furnace, though, you may need to hire an electrician.