• Blown fuses can shut down furnaces and other electrical systems.Comstock/Comstock/Getty Images
  
  A single electrical appliance or a whole set of appliances can suddenly blow, causing electricity to vanish. This blown fuse usually has something to do with an appliance placing too much strain on a particular fuse, overwhelming that fuse and causing it to short circuit. Some furnaces rely on electricity as a fuel source to generate heat while other furnaces rely on gas or some other fuel. When the fuse short circuits, it can either cause the entire furnace to shut down or can cause a component to stop working in the furnace.
  
  

Strain

• Blown fuses usually result either from an appliance putting too much strain on the fuse or by an electrical short in the system. Since some furnaces can require a lot of electricity, homeowners must ensure that they have an adequate electrical system to support the furnace. After resetting the circuit breaker and replacing the fuse, if the fuse keeps blowing, there might be an electrical short in the electrical system that supplies the electricity to the furnace. The homeowner should call an electrician.
  
  

Malfunctioning Transformer

• Sometimes the blown fuse in the furnace comes from a malfunctioning transformer. In this case, the homeowner will need a technician to come and replace the old transformer with a new one.
  
  

Overheating

• When the fuse in the furnace gets too hot, the fuse can catch on fire, causing the furnace to lose its source of electricity. The furnace must have sufficient cooling mechanisms to avoid overheating.
  
  

Wrong Size Fuse

• A furnace has a wrong size fuse that cannot handle the wattage. In this case, the technician needs to fit the furnace with an appropriately sized fuse.
  
  

Dirty Fuse

• Some fuses get dirty, which can cause the fuse to break or the engineer can establish a poor connection between the fuse and the holder, causing the fuse to fail.
  
  

Thermostat Wire

• The control board on the furnace can blow a fuse, causing the draft inducer to not start, which causes the igniter to not glow and the gas valve to not open. The fuse is designed specifically to prevent the control panel from burning up. Sometimes the fuse blows when the thermostat wires touch the metal frame of the furnace, which can deliver more voltage than the wires can handle.
  
  

Loose Wire Connections

• The furnace may not have a blown fuse but instead has loose wire connections. Voltage meters can help the technician locate the defective wire connection and repair or replace the connection.