Is your furnace not working correctly or refusing to turn on? Furnaces can have a wide variety of different issues that will limit their effectiveness or cause them to stop working. Although most furnace issues will need to be repaired by an HVAC technician, this article will show you how to troubleshoot common furnace problems so that you can at least determine why your furnace isn’t working.

Furnace Won’t Turn On

If your furnace won’t turn on when the thermostat should be calling for heat, it typically indicates an electrical issue or a problem with the thermostat itself. Electrical issues can cause a furnace to trip the circuit breaker, so this is the first thing you should check. If you have central air conditioning, you can then test if the thermostat is still working by switching it to cooling mode. If your AC doesn’t come on, you’ll need to have a technician inspect and test the thermostat. In this situation, it usually means the thermostat has failed and will need to be replaced or that the wire that connects to the thermostat is loose or damaged.

If your AC does come on, the issue lies with the furnace itself. It may be that the control board is bad, the control board wiring is damaged or loose or that the motor on the draft inducer has gone out. The draft inducer is the first thing that comes on when a furnace starts. When it runs, it triggers the pressure switch which in turn signals the gas valve to open and the burners to light. If the inducer doesn’t come on, nothing will happen when the thermostat calls for heat.

If you have someone else to help you, you should have them switch the thermostat off and back on while you listen to the furnace. If you hear gas start flowing for a few seconds and then nothing else happens, it means that the electronic igniter is bad and will need to be replaced. When inspecting your furnace, the technician will inspect and test the control board and all of the other components to determine what the issue is and what repairs your furnace needs.

Furnace Keeps Shutting Off Too Soon

A furnace that shuts down before your home reaches the right temperature usually indicates that it is overheating or has a malfunctioning flame sensor. Overheating is usually caused by a dirty air filter or malfunctioning blower motor. If replacing the air filter doesn’t fix the issue and your furnace keeps shutting down too soon, the technician will need to test the flame sensor and clean and test the blower.

The flame sensor is usually one of the first furnace components to wear out. If the sensor starts to fail, it will often have issues where it suddenly stops working and can’t detect that the burners are light. When this happens, the control board will close the gas valve and the furnace will immediately shut off. If the flame sensor is bad, your furnace will only ever run for a few seconds before shutting down.

Furnace Blows Cold Air

A furnace really should never blow cold air, as the blower doesn’t come on and start circulating air until the burners are light and the heat exchanger reaches a set temperature. If cold air is coming out of the vents, you should check the thermostat and make sure the fan is set to “Auto.” If the fan is set to “On,” it will run constantly and eventually start blowing cold air after the furnace shuts off.

If the blower is set to Auto and your heating system puts out cold air, it indicates that your furnace isn’t on. The only reason that the blower will run if it’s set to Auto and the furnace is shut off is if the temperature limit switch malfunctions and doesn’t signal the blower to shut off. The limit switch measures the temperature of the heat exchanger. After the furnace shuts off, the heat exchanger has to cool to a set temperature before the limit switch will signal it to shut off. In this situation, a technician will need to test and possibly replace the limit switch.

Furnace Heats Extremely Slowly or Runs Constantly

If your furnace runs for far longer than normal and isn’t effectively heating, it usually means that the air filter is clogged or the burners are dirty. A clogged air filter restricts how much air can flow into the furnace, which leads to it putting out almost no heat. If the burners are dirty, they often won’t fully combust the gas and will produce much less heat. This is something you can easily check for by looking at the color of the burner flames. The flames should be bright blue. If they’re yellow or orange, you’ll need to have the burners cleaned.

At AirDepot, we’ve been helping Cypress residents overcome their furnace and AC issues since 1977. We specialize in heating maintenance and repairs as well as installation, and we work on both residential and commercial cooling and heating systems. Give us a call if you need a furnace repair and our technicians will do whatever it takes to get your heating working again.

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