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Triple O Heating, Cooling, Electrical & Plumbing Blog

What Happens When a Furnace Transformer Goes Bad?


You’re probably familiar with the compressor on your air conditioning system and know that when it goes bad, the AC may need to be replaced. (Not always the case, but often.) Is the transformer for the furnace something similar? And what happens if the transformer fails? Does that also mean the end of the furnace? Or can you call Triple O to schedule furnace repair in Rochester and restore your furnace?

We’ll address these questions in this post. We know it’s not yet time to turn your furnace on, but this is information you’ll find useful in the future when your furnace goes back to work. 

What Does the Furnace Transformer Do?

First, here’s what you need to know about the transformer itself. The transformer is the component that supplies electricity to the furnace and increases or decreases the voltage of the alternating current (AC) through electromagnetic induction. For your furnace, the transformer lowers the current to 120 volts. A faulty transformer will affect the performance and efficiency of a furnace.

(If you’re thinking that this won’t apply to your furnace because it’s natural gas—it still does! The transformer sends electrical power to the blower fan responsible for moving air through the furnace to be heated and then throughout the house.) 

Signs of Transformer Troubles

Here are ways you can detect problems with a furnace transformer:

  • A failed furnace: A dead transformer means no electricity going to the furnace. This not only means the blower won’t work, but it also removes power from the control board so no part of the furnace will operate. 
  • Strange sounds: Your furnace’s transformer will make a low humming sound when working normally. If this sound increases and you notice the furnace vibrating, you need to call technicians right away. (Shut off the furnace at the furnace switch first.)
  • Tripping circuit breaker: This is one of the major warnings of a faulty transformer. If the transformer isn’t modulating the current correctly, power will surge and the breaker will trip. A single tripped circuit breaker may not be a problem. If it keeps happening, however, get pros on the job.

What Happens in the Case of a Faulty Transformer

When you call for our technicians to investigate a malfunctioning furnace, we’ll check to see if the transformer is at fault and what is wrong with it if it is the cause of the problem. Some of the transformer issues we’ll look for include:

  • A transformer that has received damage from power surges such as lightning strikes.
  • A faulty contactor. This is one of the most common causes for transformer problems. The relay is what regulates voltage flow within the transformer, and it can become stuck, which will cause the transformer to cycle inefficiently or run nonstop. Repairing a faulty relay is a basic fix for professionals. 
  • Loose wiring causing the transformer to burn out. 

Based on what we discover, we can repair or replace the transformer. For extremely old furnaces, we may recommend you have the furnace itself replaced. We’ll go over all your options with you.

Triple O Heating, Cooling, Electrical & Plumbing Is Your One-stop Shop for HVAC, Plumbing and Electrical.

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