HVAC

Connect one-on-one with an HVAC Technician who will answer your question

Connect one-on-one with an HVAC Technician

An HVAC technician repairing a gas furnace

Gas Furnace not Working?

1K views
Travis N.Verified

Maintenance Tech at Casto

Residential HVAC

★★★★★
486 positive ratings
Common Furnace Fixes

1. Switch the fan setting from AUTO to ON.

2. Change the batteries on your thermostat.

3. Replace dirty filters after 1-3 months of heavy use.

If your gas furnace has suddenly stopped working, it is essential to get it working again without spending a lot of money. There are several troubleshooting steps you can perform on your own. Sometimes even the most obvious problems can be overlooked.

Try these solutions first

  • Power – Check to make sure the electric plug is plugged into the furnace and into a power supply outlet. If there is power, check the power panel or circuit breaker box and make sure the breaker for the furnace has not tripped. If so, turn it OFF and then ON again. Sometimes there is a power switch next to or around the furnace. Check to make sure this has not accidentally been turned off.

  • Gas – Make sure there is gas coming to the unit. Sometimes the gas valve fails to open. Check to see if the gas valve is getting power while the ignitor warms up. If it is, you may need a new gas valve.

  • Thermostat – It is easy to forget to change your thermostat setting from COOL to HEAT when the seasons change and you’re not using the air conditioner anymore. If this is not the problem, then dust the inside of the thermostat, ensuring all connections are clean. Next, you should check the wiring for any broken, melted or burnt wires. If none of these solutions work, you may have to replace your thermostat. If the thermostat is in working condition, check the batteries.

  • Batteries to thermostat – If the batteries are not corroded, make sure they are new and inserted correctly. If they are corroded, replace them.

  • Air filter – A dirty or clogged air filter can cause the blower motor to work harder to push the air through. It can cause dirt and debris to end up in the components of the furnace, causing more wear and tear. Make sure you check and change your filters on a regular basis. A clean air filter will prevent the blower motor and fans from bogging down and making the furnace work harder. Replace or clean to fix this problem.

A comparison of clean and dirty air filters

Additional overlooked gas furnace problems

Check for error codes

Modern furnaces, built after 1990, have a window that shows a light on the front or the side of the heating system. This light will prove if there is power to the furnace. If there is a problem with the furnace, this light will flash a code. There are usually guides on the access panel of your furnace that tell you what the code means.

Codes are different across various brands of furnace. Codes mostly correspond with colored or blinking lights and the number of times they blink. For example, on a York furnace, three red flashes indicates a possible pressure switch caught in the open position. On Goodman units, two LED flashes indicates a problem with the draft blower or a problem with the pressure switch circuit. Usually, an internet search involving the make of your furnace and “error code” will yield information about what is wrong and how to fix it. If you’re still having difficulty deciphering error codes, ask an HVAC Expert for help in troubleshooting.

Check your glow plugs

If your furnace is an 80% efficiency furnace or higher, in all likelihood it will have a glow plug. You can check to see if your glow plugs are lit up by identifying light-like bulbs that typically turn red or orange when the furnace is fired up. If the glow plugs do not light up, they will need to be replaced, as they replace the function of the pilot light.

Check the pilot light

If the pilot light is out, then re-light it. It is easy to do this yourself. If it is a standing pilot light, then you must manually light it. If the furnace has an electrical ignition, then you should the check flame sensor and ensure there is adequate gas supply. Make sure the gas valve has not been turned off. Drafty rooms and open windows could blow the pilot light out and prevent you from being able to relight it. Shut windows that are close to the furnace. Cover up all drafts that could be directed towards your furnace

Clean the pilot light

Make sure to disconnect all gas and electric sources prior to cleaning. Clean the pilot light with a stiff wire brush and a metal file when necessary and replace any parts that are faulty. If it is an electronic ignition, replace the flame sensor or any electrical components necessary. If you have tried to relight after cleaning and the pilot flame will not stay lit, then the thermocouple may need replaced. Ask an HVAC Expert to help walk you through the process if you need help with the above steps.

A typical high efficiency ceramic glow plug
A typical ceramic glow plug used in high efficiency furnaces
A typical gas fired pilot light
A typical gas-fired pilot light used in regular furnaces


If the above common problems have been checked and your gas furnace is still not working, then there are troubleshooting tasks you can perform yourself. These do-it-yourself steps can save you time and money.

Gas furnace troubleshooting

Gas furnace does not produce heat

  1. Fuse and circuit breaker – First, turn the power off to the furnace and check the fuse in the furnace control box in the bottom compartment with the blower. If there is a pc board in the control box the fuse usually plugs into the board, if not the fuse will be on one of the transformer secondary wires. If it has burned out, replace it with the same size. If you are not experienced in troubleshooting the fuse, or replacing it, expert help may be needed.

  2. Faulty thermostat – A thermostat can prevent the furnace from producing heat and working properly. Check if the thermostat is working and replace it if necessary. Replacing the old thermostat with an energy efficient one will help keep your energy costs down.

Blower motor kicks on and off constantly        

In the machinery of a gas furnace, the inducer motor is the first to come on. Then you will see the ignitor start to glow, after which you will hear the burners kick in. The flame sensor will either keep the furnace on or keep it off. If the furnace is not staying lit, most of the time it is the flame sensor malfunctioning. You can take fine-grit sandpaper or a crisp dollar bill to clean the flame sensor. If it stays on then the flame sensor was probably just dirty. If it turns off again after cleaning, the flame sensor may need to be replaced.

You can also try adjusting the heat thermostat anticipator. This is an electrical device on the thermostat that tells the furnace blower when to come on and when to shut off. The anticipator detects when the room temperature is at the thermostat setting. By adjusting it, it will prevent the blower from kicking on and off.

Finally, a motor kicking on and off can also be caused by a faulty hot surface ignitor. Hot surface ignitors are electrically powered prongs that get very hot when activated, and are a staple of more modern heating systems. They are generally good for several years before their lifecycle ends. If you’re unsure about where to locate a hot surface ignitor or how to replace it, consider talking to an expert.

Broken or damaged blower motor belt

The belt is normally overlooked by homeowners performing maintenance themselves. A loose or damaged belt will cause a furnace to make extra noise. The noise can be very annoying, but it also costs you additional money in energy costs and eventually more costly repairs. A loose belt causes the fan to slip, not as much air to come through the vents and your home to lose heat. A loose belt should be replaced immediately. If the belt is too tight, loosen the tension so it does not break and can move more freely.

Blower fan runs constantly

First, check the filter and thermostat settings. Then, check the booster fans to ensure they are working. These fans distribute the heat evenly throughout the house.

Save time and money

A properly running gas furnace will keep your energy bills down and prevent unnecessary costly repairs. Follow a monthly maintenance routine to keep your gas furnace running in top shape.   

If you have exhausted all the above troubleshooting tips and your gas furnace is still not working, then ask an HVAC Expert for assistance.

Please type your question in the field below

8 verified HVAC Technicians are online now

HVAC Technicians on JustAnswer are verified through an extensive 8-step process including screening of licenses, certifications, education and/or employment. Learn more

Online
Phil

Consultant to Engrs, Govt & Contractors

HVAC, Ind. Reflg. Controls

★★★★★
7,553 positive reviews
Online
Matthew

HVAC Technician

Conditioned Air

★★★★★
2,014 positive reviews
Tom

HVAC Technician

Journeyman HVAC

★★★★★
770 positive reviews
See all HVAC technicians
JustAnswer in the news:
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
Web sites like justanswer.com/legal
...leave nothing to chance.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.