Heating Furnace Troubleshooting

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Things You'll Need

  • Batteries

  • Fuse puller

  • Replacement filters

Knowing how to troubleshoot your furnace will save you money on service calls.

All heating furnaces require regular maintenance to prevent breakdowns. Components of the unit work harder when dust and debris clogs the system. Cleaning the unit and replacing consumable parts such as the filter are maintenance tasks you should perform every fall before you fire up the furnace. Troubleshooting will help you solve any simple problems that may occur during the thermostat's normal operation. If at any time during the troubleshooting process you suspect a large component is broken, or you smell gas, call a service professional.


Step 1

Check to make sure the thermostat on the wall is turned on and is set to the "Heat" setting. Turn up the heat if you do not hear the compressor turning on.

Step 2

Open the thermostat and follow the wires back to the main furnace unit. Inspect the wiring for any breaks.

Step 3

Check the time and date setting on the thermostat if it is a digital unit that you have programmed to turn on at certain times. Reset the unit according to the manufacturer's instructions.

Step 4

Replace the battery if the thermostat appears dead. Inspect the wires behind the thermostat faceplate if the unit is not working.

Starting Issues

Step 1

Check the circuit breaker that controls the furnace. The circuit is usually located in your home's main circuit breaker box. Flip the breaker to the "On" position if it is turned off. Replace the fuse in the breaker box if the circuit flips to the "Off" position right away. Have the unit inspected by a service professional if the breaker continues to flip to the "Off" position. This indicates a short in the system.

Step 2

Adjust the gas valve leading to the unit so it is in the "On" position if it's turned off. A valve handle on the pipe allows you to control the flow of gas.

Step 3

Open the access panel for the unit by pressing in the button on the panel and lifting up. Look for the pilot light, which is located near the burners. There should be a blue flame if the unit is not an electrical ignition unit. Light the pilot light according to the instructions printed by the pilot light orifice.

Step 4

Remove the filter from the furnace if the unit is running but there is no hot air coming from the ducts in your home. Pull out the filters by hand. Replace the filters if they are dirty.


If you smell gas, immediately stop what you are doing and call the gas company.