How to Fix a Reversed Polarity Flashing Code Message

furnace repair

Reversed polarity error codes can be quite frustrating. For one thing, they often appear after a long period of having the device running normally. As a DIYer, you must be very cautious with these types of problems. While in some instances, it might be a problem that can easily be fixed by interchanging wires, in other circumstances, it might be a complex appliance failure. Further, the error might occur if the device is contaminated with water or other conductors.

Always practice caution when working with electrical components, and if you're not sure what you're looking at, err on the side of contacting a professional rather than risking your safety.

Polarity Basics

In theory, when polarity is reversed, power could continue flowing through the device even when the switch is off. This is the reason you must be very careful when dealing with any device that provides a reversed polarity message. When looking at any device with a reversed polarity message, be sure to test the presence of power even if you've switched it off.

In the case of fire furnaces, the problem is even more dangerous, due to their high voltage. For a fire furnace, you have three wires coming to your house from the utility. Two of the wires are hot, that is, they carry electric current. The third wire is a neutral wire. Usually, the voltage between the two hot wires is 220 to 240 volts. The voltage between the hot wires and the neutral wire is 110 to 120 volts.

When the polarity is reversed, the current in your neutral wire is running through the device. This presents the risk of getting shocked if, for instance, you touch any wire of the three and any metal on the surface of the device.

To reduce your chance of injury, always wear thick rubber gloves when working on a furnace.

Possible Causes of Reversed Polarity and Their Solutions

furnace wiring

Water Contamination

One of the major causes of reverse polarity in many devices and water contamination. If, at any point within the circuit, the hot wires come in contact with the neutral, chances are that you may see a reverse polarity error code.

This can happen if the switch is contaminated with water or other electricity-conducting liquids. The same may occur if the wires are contaminated with water anywhere along their path to the fiery furnace.

Make sure you check whether there are water leaks anywhere close to your wires. Secondly, check to see if the furnace has been contaminated by water in any way.

If the message keeps appearing and disappearing, water interference is a prime suspect, because the water could cause the error, which disappears after it dries off.

Improper Connection

hands adjusting circuits

The other primary cause of reverse polarity error code is reversed connection of power lines. In case the hot wires are interchanged with the neutral wire, there will always be current flowing through the circuit, even when it is switched off. As a result, the system will present a reversed polarity error code.

Ideally, you should start by checking the polarity of the wiring at the furnace using an AC voltmeter. While using a voltmeter, the true hot wire tested to the ground would only show voltage.

On the other hand, the neutral wire tested to the ground does not show any voltage. If it is the neutral wire that shows the voltage, the chances are that polarity is reversed.

In most cases, furnaces are usually sensitive as to which wire is connected to the switch and which to the ground. However, there are some that are not sensitive. Whichever way, checking the voltage is a great way of determining if the cables are reversed.

Check Wiring Connected to the Flame Sensor

Lastly, you ant to check the wiring connected to the flame sensor. In some systems, flame rectification systems convert AC voltage into DC signals.

In case the polarity is reversed, the DC will not make it back to the control board. As a result, the excessive signal may result in an error code.

Furnace Polarity FAQ

Reversed polarity in the sense of a fire furnace should be taken more seriously than in other instances. As we have seen, with a fire furnace, you have two hot wires, which is one more than normal.

When your furnace shows the reverse polarity code, it may mean that the wires have been connected wrongly or something has happened that has tampered with the current flow.

The only problem is that for a furnace, each of the live wires has a minimum of 110 volts flowing in it. If you happen to touch such a wire, you can be sure that you will get hit by an electric current.

While this post clearly explains the main cause of reversed polarity error codes in furnaces, there are still many questions that DIYers ask about polarity and furnaces.

Below are some of the commonly asked questions about reversed polarity and furnaces that you may find helpful.

What Does It Mean When My Furnace Says Reverse Polarity?

furnace controls

Line voltage monitoring for home furnaces was introduced in 1988. This meant that every homeowner can monitor their furnace for reversed polarity and voltage faults.

Reversed polarity flashing code helps homeowners know when the furnace is on reversed polarity. When connecting your furnace, hot wire number one must be connected to the L1 terminal while the neutral must be connected to the N terminal.

If the lines are reversed, the controls will fail to function correctly, and a flash code 9 will be experienced.

With that in mind, flash code 9 could still be caused by other factors, as discussed. There are those who experience reversed polarity error codes after several years of using the furnace.

In such a situation, the problem could be most likely with the furnace itself. You may want to diagnose the thermostat and control board. You may also find out that the problem is caused by a faulty plug.

There are instances where water contamination may cause a reversal in polarity in the primary plug.

Whichever the cause of reversed polarity, you must get rid of the problem before it is too late. Reversed polarity is a big risk that must be dealt with as soon as it is detected.

What Happens If Polarity Is Reversed on Outlet?

furnace wiring

When you get the reversed polarity error code on your furnace, there is a chance that the polarity might be reversed at the outlet.

Although rare, there are homes that have poor wiring that may result in polarity reversal. What this means is that the electrician doing the wiring for the home wired the neutral wire to the live terminal and vice versa.

This will result in a reversal of polarity, and hence, there will be power flowing through the unit at all times. When the neutral wire is attached to the live terminal and the life to the neutral, there is no way of breaking the circuit.

Even when the switch is off, the live wire continues supplying power to the device. Even when the device is off, there will still be power flowing in it, which poses a threat to the entire household.

How Do You Fix a Hot Neutral Reverse GFCI?

outlet with light

For those who are using GFCI, the polarity may also be reversed. This is very common, given that DIYers make mistakes when connecting their devices.

The good news is that you can easily fix the reversed polarity on your GFCI. The reversed polarity, in this case, happens when you connect the neutral wire and the hot wire to the wrong terminals.

To fix reversed polarity on your GFCI, start by switching power from the primary circuit breaker. Now disconnect your GFCI completely and reconnect the wires to the right terminals.

The live wire should always go to the gold screw on your GFCI. This can be achieved by simply looking at your GFCI and locating the old device. On some devices, you will find clear writing such as L1 and N1 for Live wire and Neutral wire.

How Much Does It Cost to Fix Reverse Polarity?

If your furnace shows the reversed polarity code, there are several ways you can solve it. The cost of resolving the problem will depend on the route you will take. At the same time, it depends on the cause of the reversal in polarity.

Fixing reversed polarity can be as simple as interchanging the wires in some cases, while in others, you might be needed to change the entire control board for your furnace.

The cost of repairing reversed polarity will depend on what you are solving. In the case of interchanging wires, the cost may range from zero for DIYers to $100 for those who choose to call in experts. Different electricians charge different amounts.

Regular handymen may charge you as little as $10 to interchange the wires. If you are confident in your DIY skills, the best route out would be to fix the wires yourself.

In the case that the reversal in polarity is caused by a much bigger problem such as a faulty circuit breaker, you will have to dig deeper in your pocket and purchase a new one. If you will be replacing the circuit breaker yourself, you can do it with as little as $75 for the entire process.

If you have to bring in experts to handle the process, you have to factor in the price of purchasing a new circuit breaker and the service charge. While you can get a circuit breaker for less than $70, the service charge will vary depending on those you contract.

In the case where you have to repair your thermostat sensor or replace your control board, your costs will go even higher. Replacing your thermostat will cost you well above $200, while the cost of replacing the control board may go over $500.

Why Is Reversed Polarity Bad?

Reversed polarity on any outlet is dangerous. The case is even more dangerous when your furnace is experiencing reversed polarity. The risk is that, when a plug has a reversed polarity, it still works. If you plug a device into the outlet, it may still function as if everything is fine.

When you switch the power off, it continues to flow through the device. For a heavy power device like the furnace, anyone who touches it when it is switched off could be electrocuted. It also increases the possibility of a fire outbreak.

What Causes an Open Limit Switch on a Furnace?

furnace controls

One of the other furnace problems that are related to reversed polarity is the open limit switch. The limit switch on your furnace is important since it helps avert hazards that could occur when the furnace overheats.

When the temperature on your furnace exceeds the preset requirements, the limit switch shuts the burner off. The burner stays shut off until the burner cools down and the normal operating temperature is attained.

The most common reason for limited switch opening on a furnace is plugged filters or a dirty blower. In some situations, reversed polarity may also lead to the limit switch opening.

How Do I Know If My Limit Switch Is Bad on My Furnace?

The main way of determining if your limit switch is bad is the continuous operation of your furnace's blower. The limit switch won't allow the fan to turn until the warm air reaches the right temperature.

In the same way, it shuts down when the air cools down to a certain temperature.

Can You Test Reverse Polarity with a Multimeter?

Yes, if you suspect that you may be having reversed polarity in any of your electrical outlets, you should try verifying it. Multimeters can be used to determine reversed polarity in different ways. However, the type of multimeter you are using also matters.

If you use the traditional multimeter with an arm stick gauge, it may not detect reversed polarity. On the contrary, reversed polarity may even damage the device.

Modern digital multimeters have reversed polarity displays. Alternatively, you can use the multimeter on independent terminals to determine the amount of current flowing through it.

The live terminal should always give a voltage, while the neutral and earth wires should give a small voltage or zero voltage.

Bottom Line

There are several possibilities to consider if you are receiving a reversed polarity error code. The most important factor to remember is that this is a dangerous situation. You must use protective gear to avoid getting into trouble while fixing the errors.