Grounding Or Line Polarity Fault

Grounding or Line Polarity Fault? [ANSWERED]


The circuit of your furnace not functioning properly can be due to multiple different reasons. So if you face any problem with the circuit, you cannot directly jump to conclusions. 

So wonder about grounding or line polarity fault?

To find out the fault, you will have to troubleshoot the circuit board. Using a multimeter to check the grounding and connecting the neutral wire to the ground screw should solve the issue. If the grounding is alright, check the line polarity. Reversing the polarity should fix the issue. 

Want to know the detailed procedure of how to troubleshoot the issues? And how to solve the grounding issue or the polarity issue? Well, everything you need to know is right here!

Troubleshooting Grounding

Grounding issues are frequently the most widespread issues in the field. The problem limits flame rectification and creates low or marginal flame sensing. 

If the grounding is weak, defective, or nonexistent, the furnace will not hold a flame properly. The flame will only burn for more than a few seconds. In addition to properly grounding the furnace, inspect the flame sensor for cleanliness to ensure appropriate ignition.

When providing grounding, a furnace should always have good earth ground. And it will need to follow all local and national legislation.

The furnace control is the simplest method for determining whether or not the flame signal is valid. Typically, an indicator light on a furnace will express this information. 

Furthermore, some OEMs use an LED failure code system that signals a low or marginal flame current.

A multimeter can also be used to quantify the microamps detected by the flame sensor. As a result, the number of microamps reveals how precisely the flame sensor detects the flame. Microamp values must be obtained from the manufacturer.


A multimeter will be needed for the diagnostic process. The approach is quite simple. And it should not require more time than a few moments..

Prior knowledge is only restricted to how to use a multimeter. You will also need to identify and differentiate the cables.

Step 1: Placing Meter Lead on Neutral

The first step is to connect a 1-meter lead to the neutral wire. Connect the lead cable to the neutral cable.

Step 2: Placing Meter Lead on Grounding Screw

Now is the time to find the grounding screw. Connect the opposite 1-meter lead to the grounding screw.

Step 3: Checking the Reading

Examine the multimeter reading now. Examine the resistance between the neutral wire and the ground screw.

Any reading between 0 and 0.5 AC Volts is acceptable. If the reading falls outside of this range, then the grounding is the issue.

Readings greater than 0.5 volts may result in intermittent flame failure or intermittent codes.

Solving Grounding

The ground wire is not always essential for a device to work, but it is an important component. This wire is meant to provide an alternate path for electrical current. That is in case the regular paths are unavailable.

Solving the grounding issue is pretty straightforward. 

Step 1: Turn Off the Power

As a safety measure, you must cut off the electricity. Working on a running board is dangerous. It could be fatal.

Before you begin working, make sure to turn off the main circuit. Verify that there are no issues with the electric meter as well. Problems such as the electric meter flashing 8888 would need to be resolved. before you start working. 

Step 2: Identifying Neutral Wire and Ground Screw

The control board’s transformer contains a neutral wire. You should already be familiar with it as a result of overcoming the grounding issue.

Step 3: Connecting the Neutral Wire and the Ground Screw

Finally, attach the neutral cable to the grounding screw. This ensures that your furnace is correctly grounded.

Troubleshooting Line Polarity

When a wall outlet is wrongly wired, the hot wire will be on the neutral side. Because the switch is only on the hot side. 

The identical light could be plugged in. In that case, although the switch was turned off, the lamp socket might have electricity. 

You’ll want to finish the circuit and send electricity to “ground.” For that, someone only needs to make contact with the metal.

Most furnaces are intended to operate on 115-volts of alternating current. You are allowed a plus/minus tolerance of 10%. 

So you’re fine if the volt is somewhere between 104V and 126V. The polarity of this power is a crucial factor.

These are critical to the control’s proper operation and are normally monitored via on-board control diagnostics. A flash code with “reverse polarity” may come to mind.


Let’s look at how you can determine if the issue is related to the line polarity. We’ll mostly be checking for reverse polarity on the circuit board.

Step 1: Checking the Wall Plug Outlet

Begin by inspecting the wall socket outlet that powers the furnace. Before condemning the furnace control board, make sure the power is working properly. We’d like to investigate the polarity.

The black cable is the “hot” or power line on the plug and outlet. The white wire is the “neutral” wire. And there should be no voltage between it and the ground.

Step 2: Checking Voltage

As previously indicated, there should be no power coming from the ground. If the measured voltage is larger than three volts, there is most certainly a problem. 

Other electronic equipment in the building might be the source of the problem. The appliance might be inducing a voltage into the neutral line. This must be corrected before proceeding. 

Simply continue measuring using the device. On the circuit board, “Line IN” should be “HOT” 115v to the ground. And “LINE N” should be zero volts.

On the transformer, black should be 115 volts and white (neutral) should be 0 volts. The transformer’s output should be Red = 24v and Blue = 0v. They should both be linked to the earth.

Step 3: Verifying Power

Now that you’ve checked the machine’s power, a malfunctioning control board is most likely the source of the reverse-polarity problem if it persists.

Solving Reverse Polarity

Now with the diagnosis, you know you have a problem with reverse polarity in your circuit board. So now you have to fix the reverse polarity. 

Step 1: Making Sure the Furnace is Grounded

We have already explained how to determine whether or not the furnace is grounded. And how it can be resolved.

If your furnace is not grounded, you will be unable to address the reverse polarity issue.

Step 2: Turning the Power Off

This is undeniably true. Turn off the furnace electricity as a precaution.

The safety aspect of turning off the electricity necessitates a distinct method. Make certain that there is no electricity in the furnace. 

Hopefully, there will be no problems with the circuit breaker not seating properly. But if there are issues, resolve them prior to starting to work. 

Step 3: Identifying the Low Voltage Wires

Low voltage wires are connected to the control board. They are the black and red cables coming in from above, respectively. 

The conductors are housed within the secondary transformer.

Step 4: Swapping the Low Voltage Wires

You have turned off the electricity and located the low voltage wires on the secondary transformer. Now you must connect these two wires.

The two low-voltage wires will swap positions. 

But remember to avoid inverting the black and white wires. Changing the black and white wires will have an impact on the circuit breaker box. This will have an effect on the circuit breaker panel. 

Because it is more difficult, this should be avoided. And with that, your reverse polarity should be alright. 


What does grounding or line polarity fault?

Line voltage difficulties are caused by polarity/ground faults. Because most circuit boards are polarity sensitive, the fan is not driven by the board. Voltage spikes are a regular concern when the power goes off, and they have the potential to fry circuit boards or wires.

What causes reverse polarity?

Reverse polarity occurs when a plug is wired incorrectly. This happens when the “hot” wire, sometimes known as the black or red wire, is connected to the neutral terminal and the neutral terminal is linked to the “hot” terminal.

Can a bad outlet cause reverse polarity?

Yes, a bad outlet can cause reverse polarity. Improper hot and neutral wiring at an outlet is one of the most typical reasons. Reversing the polarity of an outlet’s wiring is a straightforward fix. Even anyone inexperienced can do it.


And with that, we know how to find out grounding or line polarity fault. Troubleshooting the circuit board will bring light to the issue. 

Solving both grounding and line polarity is fairly simple. Just maintain proper safety measures and follow our guidelines. 

Good luck!

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