flash codes for gas furnacesGas Furnace Troubleshooting and Repair - Flash Codes - In the extreme cold weather, there is nothing worse than losing your heating system. Here are some basic tips for checking basic things for the average person, to, hopefully, make a quick fix. A quick fix, so you do not have to suffer until an HVAC repairman comes.


Gas Furnace Troubleshooting and Repair - Flash Codes

Diagnostic Flash Codes for Gas Furnace Troubleshooting

Refer to the article link above for additional gas furnace troubleshooting tips and advice. On modern electronic ignition gas furnaces, there are fault codes that can flash on an electronic module or a circuit board located inside the gas furnace. These fault codes (not always fault by the way) can help an HVAC tech repair the gas furnace more quickly than if he had to start at the beginning of the sequence of operation for the gas furnace.

All manufacturers are different, especially the ignition control module or circuit board manufacturers. Not every OEM or furnace manufacturer make their circuit control boards or ignition control modules. Many of the gas furnace manufacturers will purchase these from third parties and install them in their gas furnaces. The following is simply a generic guide to assist you in finding a problem. However, we always urge you to read our disclaimer and to contact a professional HVAC Technician to diagnose and repair any gas furnace.

Gas Furnace Troubleshooting and Repair - Flash Codes | Fault Causes

Remember, there is a normal flash when everything is good with the gas furnace. Just because the module or circuit board is flashing doesn’t mean there is a problem. A steady flash typically means everything is okay. There are problems when you have intermittent flashes, and when that occurs, you usually will have a problem. Most manufacturers will put a flash code chart on or near the ignition module or circuit board. This flash code chart will describe the problem. Problems can be in one of five areas for the gas furnace:

  1. Ignition Problem
  2. Blower Problem
  3. Inducer or Pressure Switch issue
  4. Gas Valve Problem
  5. HVAC Accessory Problem (accessories can be an electronic air cleaner or a humidifier)
Gas Furnace Troubleshooting and Repair - Flash Codes | Components Faults Explanation

Within those fault codes, you can have a host of issues with various gas furnace components such as:

  • Bad switch. The furnace has many different safety switches inside it, including a pressure switch and various temperature switches. Some of these are both automatic reset and manual reset. Automatic reset switches are not so bad the problem is the manual reset switches. When a homeowner continuously resets a manual reset temperature switch, they are creating a possibly dangerous situation. Especially after the switch is manually reset because it tripped over a serious problem occurring. And the problem does not necessarily mean it is the switch that is the problem. However, it could be another component or issue causing the switch to trip. These switches do fail from time to time. However, they are there for safety reasons, and constantly resetting them presents a possible danger to the occupants. The matter needs to be looked at closer to make there are no further problems beyond a bad switch.
  • Flame problem or a sensor problem?
  • Power problem?
  • Module or circuit board problem?
  • Additionally, other problems outside of the electronics that are causing the malfunction?

Gas Furnace Troubleshooting and Repair - Flash Codes

Ignition Control Module by White-Rodgers (Now Emerson Electric)

All furnace control boards allow for some watchdog ignition lockout after several trials for ignition failures. The purpose being safety. When a furnace is trying to fire, it releases gas from the main valve and attempts to light electronically. Too much gas build-up is why it locks out for some time. This watchdog lockout allows for the gas to dissipate. This time delay ensures excess gas does not become a hazard and cause an explosion.

Gas Furnace Troubleshooting and Repair - Flash Codes

Nearly every manufacturer has different flash codes. Within the manufacturers, the flash codes can be different from one furnace to the next. Therefore, it is nearly impossible to describe every flash code event for every furnace for every manufacturer.

If your furnace fails and you find the flash code, it is very likely the flash code instructions are on a label inside the furnace panel. Or on the ignition control module if you have a module. See the photo, and you will see on the left side of the module a diagnostic list of flash codes.

Again for that particular electronic ignition module, those are the flash codes. However, the odds are the same flash codes list in the photo are not the same flash codes for your gas furnace.

By the way, most furnaces will not run when you remove the panel. That is a safety factor for obvious reasons. With gas furnaces, it is always best to be safe. Especially when you do not understand everything about the gas furnace, a little research and you will find news stories of homeowners who worked on their gas furnace. In the story, there was an accident, and people got hurt or worse.

Gas Furnace Troubleshooting and Repair - Flash Codes | Service and Repair

I responded to a call one January night when it was around 15° F. for an emergency no heat call. The homeowner had previously reset a manual switch (several times), which was a very important safety switch.

This switch in HVAC terminology it is a spill switch or a hood switch. It is placed near the ventilation for the flue gases to allow atmospheric air to mix with the flue gases. It helps gases go up the flue easier.

The carbon monoxide detector started sounding the alarm. Furthermore, the family can thank God they had a carbon monoxide detector (many people do not), and it was functioning properly.

It turned out that during the summer months, a bird had built a nest at the top of the chimney. It was partially blocking the flue gases escaping the top of the chimney. The flue gases backed up and started spilling out of the hood.

That is where secondary atmospheric air should be venting into the flue gas stream and not out of it. The switch worked as designed, but because the homeowner kept resetting the manual switch, it created a serious hazard that could have led to death.

The homeowner had figured out the problem using diagnostic codes on the board. They traced the problem out to that switch. That was a gas boiler, by the way. By resetting the switch, he placed his family in grave danger. However, luckily, everything turned out good, and everyone was healthy. So when you do read the flash codes and try to fix it yourself, is it fixed?

Gas Furnace Troubleshooting and Repair - Flash Codes | Conclusion

That is why it is necessary to call a professional and let them resolve the issue. The professional can resolve it safely and efficiently before you reset that manual safety switch for the umpteenth time. I’m not trying to scare anyone. However, from my experience of several years in the field working as an HVAC Technician, I have observed some real disasters that could have been avoided had they consulted a professional.

High Performance HVAC

Gas Furnace Troubleshooting and Repair - Flash Codes

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