What Those Error Codes Mean on Your Furnace

When you run into furnace problems, their annoying red error codes let you know it. But what are they trying to say? Are they just there to mess with you? What do those error codes mean on your furnace? Is there any truth to that “crazy red light” theory? Let’s decode those frustrating read error codes. There are so many things that can go wrong with a furnace. Every single one of them has its error code. And when something goes awry, your boiler will let you know in no uncertain terms: With a big ol’ red light and an even bigger red code. Many people think these error codes are just added for good measure; perhaps as part of some sick joke by engineers who like to mess with the general public. In reality, however, these error codes have a very specific meaning…

Error Code 21 – Furnace Intake Valve Shuts Too Soon

This error code means that the furnace intake valve shut too soon. It may be shutting itself before the burner has started. This can happen if the gas pressure in the furnace isn’t high enough. It can also happen if there isn’t enough airflow through the furnace, if the filter is dirty, or if the filter is clogged with lint. If this happens in the middle of the heating season, check to see if the incoming gas pressure is set high enough. If the pressure is fine, then the problem could be that there’s not enough air flowing through the furnace. To check for this, open the furnace intake door and look to see if there’s a lot of lint inside. If there is, clean it out. If there isn’t, and you can’t find any other problems, call a furnace repair person to check out the furnace.

Error Code 23 – Furnace Exhaust Opens Too Late

This error code means that the furnace exhaust valve opened too late. It may not have opened when the burner shut off, or it may have stayed open too long, causing a furnace exhaust backdraft. The pressure inside the furnace dropped too low to open the valve, or it stayed that way too long, causing a backdraft. The problem could be a stuck exhaust valve, an incorrect adjustment, a faulty pressure switch, or a blocked vent pipe. If the furnace has a continuous pilot flame, see if it blinks. A blinking flame means that the pressure switch is working, and the valve may be stuck. If the flame doesn’t blink, the pressure switch may be faulty. Call a furnace repair person to check it out, and have him clean the vent pipe.

Error Code 32 – Furnace Purge (Recirculation) Problem

This error code means that there is a problem with the furnace purge (recirculation) rate. The furnace is purging itself of carbon monoxide. If it’s not doing it fast enough, or if it’s not doing it at all, this error code could appear. The problem could be that the recirculation blower isn’t operating, that the control is malfunctioning, or that there’s a blockage in the gas line. If the blower isn’t operating, check the circuit breaker or the furnace circuit board and replace the fuse if necessary. If the control is malfunctioning, replace the fuse. If the problem is a blockage, clean the gas line. If none of these things work, and the error code keeps coming on, call a furnace repair person.

Error Code 34 – Furnace Sensor Malfunction

This error code means that the temperature sensor isn’t operating properly. It’s telling the furnace that the air in the room is hotter than it is. It may be stuck in the “on” position, or it may have been damaged by high heat. It could also be the sensor on the heat exchanger. If the sensor is stuck in the “on” position, turn it off and clean it. If it was damaged by high heat, replace it. If it’s the sensor on the heat exchanger, call a furnace repair person. If it’s the sensor on the blower coil, turn the furnace off and wait until the sensor cools off. Then turn the furnace on and wait until it finishes its cycles.

Error Code 35 – Furnace Burner Doesn’t Turn On or Stays on too Long

This error code means that the furnace burner didn’t turn on at all or that it stayed on too long. It may be that the gas pressure is too low, or that the gas pressure is too high. The pilot may be either too low or too high. Or the gas flow to the furnace may be blocked. If the gas pressure is too low, check the outside gas supply to see if it’s turned on. If the pressure is too high, turn down the regulator. If the pilot is too low, turn up the pilot adjustment knob. If the pilot is too high, turn down the pilot adjustment knob. If the gas flow to the furnace is blocked, carefully clean the line. If none of these things work, and the error code keeps coming on, call a furnace repair person.

Error Code 38 – Furnace Electronic Control Malfunction

This error code means that the electronic control malfunctioned. It could be that the control didn’t turn on, that it turned off too early, or that it turned off too late. It could also be that the control is not responding to any of the sensors. Or it could be that the control is receiving incorrect data from the sensors. If the control didn’t turn on at all, check the fuse on the circuit board. If the control is turned off too early, turn it back on. If the control is turned off too late, check the circuit board for any blinking lights. If the control is not responding to the sensors, check the circuit board for any blinking lights. If the control is receiving incorrect data from the sensors, turn off the furnace and wait about an hour to see if the sensors reset themselves.

Error Code 39 – Furnra Electronic Or Flame Detection Problem

This error code means that either the furnace flame sensor or the furnace electronic flame detection malfunctioned. It could be that the sensor didn’t open when the furnace ignited, or that it opened when it shouldn’t have. Or it could be that the sensor didn’t close when it should have. If the sensor didn’t open when the furnace ignited, check to see that it’s clean and that it’s not blocked by lint. If it didn’t close when it should have, clean the sensor and make sure that nothing is blocking it. If none of these things work, and the error code keeps coming on, call a furnace repair person.

Final Thoughts

When it comes to your furnace, it’s important to know what those error codes mean on your furnace so that you can know when to call a furnace repair person. While it can be tempting to try to diagnose the problem yourself, be sure to remember that these systems can be very dangerous. We recommend hiring a professional to help you out and to make sure everything is done properly. And remember – don’t panic if your furnace breaks down. Instead, go through the list of error codes above and see if you can figure out what’s wrong. If you can’t, don’t hesitate to give us a call. We’d be happy to help you out with any furnace problems you might be having!