How To Tell If Furnace Fuse Is Blown (Every Possible Way With DIYs And Tips)

Though there can be many problems regarding a furnace, a blown fuse is the most common one you’ll ever encounter. So, how to tell if furnace fuse is blown?

First, check the power of the furnace. Second, check whether the circuit breaker is functioning or not, and finally, locate the fuse box and check its condition as well.

A fuse consisting of a thin metallic wire in the middle tends to blow when there’s a high surge current passing.

So, in order to check for a blown fuse, one has to maintain some helpful tips (discussed here) that will help a furnace owner conclude about the state of the furnace fuse.

5 Facts for How to Tell If Your Furnace Fuse Is Blown

Furnace Fuse

There are many protective elements in the household that try to keep your electrical appliances safe from any kind of disturbances. In order to check whether the furnace fuse is blown or not, cross-check the discussed points.

1. Check the Power Supply

The first thing in the process of blown fuse analysis is to make sure the connections to the furnace are still operational. Once you’ve checked the connections, observe whether the furnace thermostat is in heat mode with a suitable heating temperature.

After that, locate whether the power knob of the furnace is in the ‘ON’ position or not. If you find that your furnace fire still hasn’t shown up, then the problem might be internal (which leads to the problem of protective elements).

2. Check the Circuit Breaker

The first protective element to consider is the circuit breaker, which normally trips when there’s a high current flowing through the wire.

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While checking the circuit breaker, if you observe that the coil has tripped, then putting it back to the original upward position should’ve powered the furnace.

Is the furnace still not operational? Then it’s time to move on to the vulnerable protective device of the electric circuit, the fuse.

3. Locate the Fuse Box and Check the Fuse

Now, it’s time to locate the fuse of your furnace. Depending on the model of the furnace, the location of the fuse might vary, and we suggest you check your user’s manual.

But, in most cases, a fuse is most likely to be located inside the main electricity board, whether it’s an electric or gas furnace. Once you’ve opened the board, you’ll locate the furnace fuse box.

Open the fuse box and then finally, you’ll locate the presence of the fuse element for protection purposes. As mentioned earlier, most fuses consist of a thin metal wire which will blow in surge current.

Additionally, most fuse covers are transparent which allows people to see the thin metal wire without opening the lid. But what does a blown furnace fuse look like? If you notice that the metal bar is broken, the fuse seems brownish, or the wire is blown, then you might have to change the fuse to operate your furnace.

Good fuse vs blown fuse

Good fuse vs blown fuse

4. Measure the Resistance of the Fuse

Unfortunately, there’s some fuse that doesn’t come with a transparent cover and the wire is troublesome to detect from a side view. Hence, one can apply some practical knowledge to measure resistance.

If you have a multimeter, set the knob on the meter to resistance and connect the two probes to the two terminals of the fuse. As the fuse contains thin metal wire, the resistance reading will be negligible.

But, if the multimeter reading shows OL (Over Limit), you have to be certain that your furnace’s fuse is blown and is no more operational.

Testing a Fuse with the Help of a Multimeter

Testing a Fuse with the Help of a Multimeter

5. Testing a Fuse Without the Multimeter

There’re various methods to test a fuse without the help of a multimeter, such as:

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Using a Light Bulb

Connect the fuse in series with the light bulb and a reliable voltage source (a battery). When the connection is fulfilled, the illumination of the light bulb will ensure that the fuse is safe. Otherwise, you can conclude it’s a blown fuse that needs replacement.

Using a Voltage Tester

A voltage tester comes in the form of a screwdriver which has a bulb at its end. When the tester comes in contact with a phase wire, the bulb lights up.

So, connect your suspected fuse with a phase wire and hold a voltage tester at the end tip of the fuse. If the bulb inside the tester doesn’t illuminate, then the fuse has gone bad.

Using a Non-Contact Voltage Detector

The major difference between a voltage and a non-contact voltage detector is that you don’t have to place the detector at the end of the fuse.

It has a light bulb inside the detector which will illuminate when it comes close to a phase wire. Additionally, it also has a beep sound feature for better results.

To establish such a result, you need to connect the fuse with a phase wire and closely held the voltage detector. If the light bulb lights up or the detector makes a beeping noise, then the fuse is functioning well.

How Much Does It Cost To Replace A Blown Furnace Fuse?

If you wish to replace the blown furnace fuse all by yourself, then the cost of a new fuse might be between 10 to 20 dollars. But, if someone wishes to seek professional help, then the labor cost will cost some extra charges, such as $65 to $100 per hour.

For those who want to carry the task all by themselves, embrace your fear of electric shock. The process is simple, just take out the blown fuse and reattach it with the new one. For your convenience, here is a tutorial on how to replace the blown furnace fuse

Frequently Asked Questions (FAQs)

Are all furnaces installed with internal fuse elements?

Most furnaces are installed with small fuse elements such as a 4 or 5 amps current limit to protect the circuit board and other internal parts from an overload of current or voltage.

What is the significance of the fuse current rating?

For example, if you have a 10-ampere fuse installed in your furnace, any current greater than 10 amperes will immediately blow up the fuse thus protecting the internal circuit of your appliance.


So, how to tell if furnace fuse is blown? The process should start with checking the connections, and circuit breaker and finally end up checking the condition of the fuse.

Furthermore, there are mainly two ways to ensure a blown fuse. It’s either by directly looking at the thin wire, or using a multimeter to check the resistance value.

After ensuring that the fuse has blown, the replacement cost will vary whether you choose to seek professional help or not. Hence, now that you have a clear-cut idea about furnace fuses, go and check yours!

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