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How to Fix a Furnace 3/5 AMP Fuse that Keeps Blowing

fixing a blown furnace fuse


Why Does my Furnace Fuse Keep Blowing?

A fuse in a furnace can keep blowing because of too much strain on the circuit, incorrect fuse size or loose wiring.

Do you have a furnace that keeps giving you trouble? One of the common problems faced by many people is the fuse blowing out in their furnace. If you are also facing this issue, read on to know why this happens.

If the fuse blows out too often it indicates some serious underlying issue. This needs to be resolved at the earliest to prevent any kind of fire hazard. The common reasons for the fuse blowing out are listed below.

  • Overloading the system

If your furnace is strained too much through an overload of current or power, the fuse could blow out.

  • Fuse size not correct

If you are using a fuse that is of a smaller size than what is required for the furnace it could keep getting blown. It is important to use fuses of the correct size.

  • Loose wires

Sometimes if any of the sites in the circuit have a loose contact, it can cause the circuit to malfunction. This, in turn, can cause the fuse to get blown repeatedly. The sites have to be fixed correctly to address this problem.


How do I know if my Furnace Fuse is Blown?

How do you identify if the fuse is blown in your furnace or not? Most importantly, you should be able to identify the fuse correctly. It may sometimes be quite tricky to identify the fuse in your furnace.

The furnace fuse is essentially a short piece of wire inside it, of varying size and composition

When the voltage level increases too much, the fuse-wire will melt. This will terminate the connection to the furnace instantly, switching it OFF.

  1. Disconnect the furnace from the main power supply.
  2. Identify the fuse in the system and carefully remove it.
  3. A wire that is damaged can cause the fuse to blow.
  4. Use a multimeter to check for a blown fuse.
  5. Note down the reading of the resistance. Ideally it should read between 0 to 5 ohms.


Why Does my Furnace Trip the Circuit Breaker?

An overload to the circuit can cause a furnace to trip the breaker.

If your furnace tripped the circuit breaker, then you need to make sure that it was just a one-off incident. Any kind of problem inside the furnace may have caused this tripping. If you turn the circuit breaker back on and it doesn’t trip again, then it is can be brushed off as a single episode.

If the circuit breaker keeps tripping frequently you need to understand the root cause of the issue. Some of the common causes of this problem are listed below.

  1. If the electrical supply passing through your furnace is way more than what it can handle, the circuit breaker might trip.
  2. An overloaded circuit can also cause the circuit breaker to trip. For example, if the circuit has a furnace as well as some other heavy appliances connected to it, the circuit can get overloaded.
  3. To solve this issue, you should call in an electrician to set up a new circuit and split up the appliances connected, between these circuits.


Fuse Safety Tips

So, if you are using a furnace at home what sort of precautions should you take while handling the fuse wire?

Here are some important safety tips to be followed to ensure protection for you, the furnace and the surrounding environments.

  • Safety precautions

Remember to call in a certified electrician to perform any sort of electrical work. Do not try to do any wiring or circuitry work on your own especially if you are not familiar with it. It could lead to dangerous situations.

  • Electrical shock

If the fuse blows out, you should turn off the circuitry.

  • Identical fuse

After removing a blown fuse, when you are replacing it, make sure that the new one is identical to the old one.

  • When buying a new fuse, ensure that it is made of the same material, has the same power and thickness as the origin alone.
  • Metal objects

Don’t bring any metal objects close to the circuit. Metals are good conductors of electricity and you may experience an electric shock if it comes in contact with a live wire, which could be very dangerous.

How to Keep a Fuse from Tripping

When a fuse trips frequently, it’s usually caused by a fault with either the furnace or circuitry. It’s important to identify the underlying cause of this issue by inspecting the condition of the wiring.

  1. Check the wiring. Most often one of the wires could be damaged. This could lead to overcurrent in the circuit.
  2. Check the wiring thoroughly and replace them if they are damaged. This could prevent the fuse from tripping.
  3. A metal object such as a nail could be caught in the wires; which can cause the fuse to trip.
  4. Check the amperage of the circuit. If a heavy current is passing through the wires, the fuse might trip. Ensure that the voltage and current remain within the normal limits in the circuitry.
  5. Make sure that multiple components are not connected to the same circuit. For example, if you have a television, fridge and a furnace, it would be a good idea to connect them to separate circuits that can prevent overloading.


How to Replace a Blown Fuse on a Furnace

Now that you know how to identify a blown fuse, you will need to replace it. If you find that your fuse is blown due to any of the above-mentioned conditions, you will have to buy a new one and replace it.

It is very simple to replace a fuse wire in a furnace.

  1. Switch off the electrical circuit. Make sure that the power supply is turned off. This is very important as it can lead to electrical shocks otherwise.
  2. Turn off the circuit breaker. This can help prevent any electricity from passing through the circuit.
  3. Check the amperage using an ammeter. This is to ensure that there is no current passing through the furnace.
  4. Identify and remove the fuse which is blown. This fuse will have a blackened look.
  5. The new fuse wire should be of the same type and length. Make sure that it is identical to the old fuse wire.
  6. Replace the new fuse wire in the exact slot and make sure that the ends are connected firmly.


Furnace Control Board Fuse Keeps Blowing

If you find that the fuse in the control board connected to your furnace keeps blowing out, have the thermostat wires inspected for damage.

  1. The wires that connect to your thermostat are the ones that cause this fuse blowout. Check those wires properly for any sort of damage.
  2. If any wires are passing outside the house or are exposed to sunlight, check these sites properly. These are the most vulnerable wires as exposure to sunlight can cause wear and tear in them.
  3. Check the sites connecting your outdoor unit, as well as any other wire connected to the furnace. Wires which are damaged will cause overloading in the circuit. This can cause the fuse to blow out.
  4. Replace the damaged wires immediately to prevent this problem.


3A Fuse on Circuit Board Keeps Blowing

The 3A fuse on a furnace circuit board can keeps blowing because of a faulty transformer or damaged thermostat wiring.

  • Every furnace circuit board has an inducer and if it is faulty it can cause a fuse to keep blow continuously.
  • Check the transformer for any faults. If the transformer is broken or damaged, then it could also cause the fuse to blow out. Replacing the transformer can help resolve the issue.
  • Check the voltage readings using an ammeter. If the readings are abnormal, then the issue lies with the overloaded circuit.
  • Have an electrician change the circuit.
  • Check your furnace thermostat wires to ensure that there is no breakage. In most of the cases, these wires are the culprit which causes the fuse to blow out.


5A Fuse on Circuit Board Keeps Blowing

The 5A fuse on a Furnace circuit board can keep blowing due to damaged wiring, or a faulty compressor unit.

  • Check for damage to the cables. The thermostat cables usually run outside your house.
  • Check to see if any wire has shorted out.
  • Check the compressor unit for any damage. If the compressor unit it can cause a fuse to blow.
  • Check the wiring between the air handler and the consensus unit. If this wire has a low voltage capacity it could cause problems to the fuse. You can use a voltmeter to check the voltage running at each point.
  • Ensure that the voltages are within the specified ranges.

Ernie Lo

Ernie Lo is a qualified web designer and web developer. He works as an IT support technician and website manager at Benleigh Vending, and he also fixes vending machines.

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