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3 Possible Causes of a Blown Furnace Fuse

by Feride Halma

Most modern furnaces, whether gas-powered or electric, have an internal low voltage fuse that protects the circuit board from power surges. When the furnace fuse has blown, your furnace will refuse to run when you try to turn it on at your thermostat. There's no way to completely prevent a blown furnace fuse, but understanding the reasons for this problem can help you recognize it in your own furnace. Here are three possible causes of a blown furnace fuse.

1. Dirt and Dust Buildup

If you've used your furnace for years with little cleaning or maintenance, it may have a secret enemy: dust. Furnaces are prone to dust buildup since central HVAC systems circulate air from every part of the house. Hidden dirt, pet dander, and other pollutants that aren't caught by the furnace filter may land on the sensitive internal components of a furnace.

Dirt on a furnace circuit board can cause overheating when capacitors and other components on the board can no longer release heat effectively. Dust and dirt can also be conduits for electrical shorts and arcing. Annual furnace inspection and cleaning from a professional HVAC contractor prevents dust buildup that could blow a fuse or cause other damage to your furnace.

2. Failing Safety Valve

If you have a gas furnace, your furnace fuse problems may be related to another component: the safety valve. The safety valve is a critical part of the furnace ignition loop that delivers gas to the pilot light. Without regular professional maintenance, soot and dust can clog the safety valve over time. If the safety valve gets stuck shut, the gas buildup can cause overheating that may blow your furnace fuse.

3. Leaks and Condensation

It may sound unlikely for water to reach the fuses inside your furnace, but it can happen in unexpected ways. For example, a major plumbing leak above your furnace can easily drain down into the casing and cause damage.

If you live in a humid climate, problems can even arise when condensation from the air collects inside your furnace. Modern furnaces have a condensate drain to remove excess condensation, but the drain can become clogged with dirt and algae. If you notice water leaking from your furnace, hire an HVAC technician to inspect the condensate drain before a blown fuse occurs.

A blown furnace fuse should be a rare occurrence that protects your home from the effects of a power surge. If your furnace blows its fuse continuously, get in touch with a local HVAC contracting service to diagnose and repair the problem.