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What Do These Furnace Error Codes Mean?
Posted On: September 21, 2024
Furnace error codes are diagnostic signals that help identify problems with the furnace's operation. Each code represents a specific issue that needs to be addressed, typically related to components like the thermostat, sensors, or burners. Here's a breakdown of some common furnace error codes:
1. Error Code 1 Flash:
- Issue: Furnace is in a lockout mode.
- Meaning: This typically happens after three failed ignition attempts. The furnace will shut down for safety reasons.
- Solution: Reset the furnace or call a technician to check the ignition system.
2. Error Code 2 Flashes:
- Issue: Pressure switch stuck closed.
- Meaning: The pressure switch monitors the venting system. If it’s stuck, it means the furnace might be having issues with the venting process.
- Solution: Check for blockages in the vent pipe or replace the pressure switch.
3. Error Code 3 Flashes:
- Issue: Pressure switch stuck open.
- Meaning: The switch is open when it should be closed during normal furnace operation.
- Solution: Ensure the vent pipes are clear, and the switch is functioning properly.
4. Error Code 4 Flashes:
- Issue: Limit switch open.
- Meaning: The limit switch is a safety device that shuts off the furnace if it overheats.
- Solution: Check for restricted airflow due to dirty filters or obstructed vents.
5. Error Code 5 Flashes:
- Issue: Flame sensor failure.
- Meaning: The furnace cannot detect a flame, which could indicate a dirty or faulty flame sensor.
- Solution: Clean the flame sensor or replace it if necessary.
6. Error Code 6 Flashes:
- Issue: Ignition lockout.
- Meaning: After three failed ignition attempts, the furnace will enter lockout mode.
- Solution: Check the gas supply and ignition system, and reset the furnace.
7. Error Code 7 Flashes:
- Issue: Gas valve stuck closed.
- Meaning: The furnace cannot get the gas needed for combustion.
- Solution: Inspect the gas valve and ensure it’s operating correctly.
8. Error Code 8 Flashes:
- Issue: Low voltage issue.
- Meaning: The furnace is not receiving adequate power to function properly.
- Solution: Check the electrical connections and wiring to the furnace.
Each brand of furnace may have different error codes, so it's important to refer to the furnace’s manual for specific meanings or call a professional HVAC technician if you're unsure about any particular code.
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See What Our Customers Are Saying:
Aug 8, 2025
We are very happy to recommend this company to everyone. Our furnace broke down on Sunday morning. We phoned them and before noon Grant the owner showed up. He worked on the furnace for about a hour not wanting to give up to fix the problem. The furnace was 17 years old. I was the one talking about replacing it. End result was the next day it was all done. On the Sunday Bob came over with heaters to warm up the house. We decided to replace the water heater at the same time. Thanks Grant for the excellent work. Thumbs up.
Aug 8, 2025
Right on time. Explained how to work the HRV in a different way so the house would not be so dry. Changed my whole house water filter for me as well. Friendly, helpful, caring service!
Feb 18, 2025
Very pleased with the professional service that TwinTech Heating and Cooling provided in replacing my furnace. I got several quotes from different service providers. Their price was excellent and they explained the features very well. We are very glad we went with TwinTech and highly recommend their services.
Feb 18, 2025
We were new homeowners in need of a second opinion. TwinTech Heating & Cooling were Amazing and professional. Very knowledgeable and great service all around. Recommend to anyone looking for honest and reliable services. Treated with respect and care. Thank you Greg, Mitch and Bob!
Feb 18, 2025
TwinTech is an excellent and honest company! I called them for a second opinion after being told by another company that I needed to replace my furnace. Turns out this was not the case at all! I did not need a new furnace. TwinTech did not push to make an unnecessary sale and saved me from a huge expense. Bob and Mitch were extremely professional and above all honest! I definitely recommend TwinTech!
Feb 18, 2025
Amazing experience with TwinTech Heating & Cooling! Their team was professional, knowledgeable, and efficient from start to finish. They installed my new furnace quickly and left everything spotless. The technicians took the time to explain everything and made sure I was comfortable with the system before they left. Great customer service and fair pricing. I highly recommend them for anyone needing HVAC services!
Feb 18, 2025
Great experience all around. Bob was sharp and easy to talk to, and Greg handled the installation perfectly. Would hire them again in a heartbeat.
Aug 17, 2024
I returned from vacation to find my AC unit on the Fritz. After calling way too many places I connected with TwinTech. Ive used the company in the past for my furnace so I was happy when I recognized Greg at my front door. Hes great and the service is always top notch. Id highly recommend using twintech for honest, superior service in the Durham region. Thanks!
Aug 13, 2024
I called Twin Tech when my air conditioning stopped working. Greg came over to diagnose the issue - the same day. He was able to diagnose the issue and resolve it quite quickly. Although it was a quick fix, Greg was very thorough in explaining the issue and provided great advice. Not to mention, I felt very comfortable having Greg in my home - which I consider very important when hiring a service provider. Twin Tech will be my go-to from now on. Thank you!!
Aug 12, 2024
Just hired TwinTech Heating & Cooling to do an A/C Unit removal & reinstall to allow for landscaping access on the side of my house, and they were wonderful!
Bob, Greg & Mitch make a great team! Quick appointment times, super knowledgeable, expert troubleshooting capabilities & very customer service oriented.
I would highly recommend them for all of your HVAC needs! Great job guys!!
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