Common Furnace Issues and Replacement Parts

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Common Furnace Issues and Replacement Parts

Written by: Aaron Huntley



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It’s that time of year again when we cross our fingers as we flick the furnace switch to “ON” and hope that nothing is broken. After a year of sitting idle, the opportunity for clogs, malfunctions, seasonal damage, or just plain routine maintenance is high. 

Today we’ll cover some of the most common furnace problems you’ll likely encounter during a troubleshooting or seasonal maintenance check. Some of these issues can be fixed with a simple replacement part, others require assistance from an HVAC professional. Please call your local HVAC technician if you encounter any issues that are above your skill level.

Issue: Thermostat Isn’t Working

One of the easiest and most common malfunctions starts with the thermostat. A good giveaway for this is your fan constantly running or not running at all. 

Start by making sure the thermostat display is on and lit. If not, the batteries might be dead or a fuse may be blown. If this isn’t the case turn off the breaker connected to the thermostat and remove the cover to look for debris build-up or a potential programming issue.

Replacement Parts

Issue: Ignition / Pilot Control Won’t Start

Typically there are two types of ignition systems for gas furnaces and it’s important to keep an eye on it regardless of which one your furnace has. An intermittent pilot system utilizes an electronically controlled high-voltage spark to ignite the pilot and burners when the thermostat calls for heat. 

A hot surface ignitor system uses a resistance heating element, similar to the filament on a light bulb, to ignite the burners. Both are susceptible to maintenance requirements. 

Some common malfunctions you’ll encounter are drafts or clogs in your heating system that result in your pilot light blowing out, malfunctions / faulty ignition wiring causing the ignitor to fail, or voltage in the electrical circuit being set too high. 

Luckily both types of ignition systems have straightforward replacement parts once the issue has been identified. Hot surface ignitors typically need to be replaced every 3-5 years before eventually cracking from continued use and come with an affordable price tag. 

Intermittent pilot systems require a new module but can also be an affordable replacement part. (You may need help from an experienced technician installing furnace replacement parts. When in doubt always consult a professional).

Replacement Parts

Issue: Rapid Cycling Problems

Rapid cycling occurs when your furnace continuously turns on and off too quickly before heating the home to the set temperature. Typically this is a sign of a dirty/worn-out air filter.

If a new filter isn’t helping the issue, it could be a sign of the blower motor and/or belts need to be replaced. Do NOT try to replace those parts yourself, call an HVAC professional to assist with installation.

Replacement Parts

Issue: Gas Furnace Blower Runs Continuously

This is another common issue most homeowners will encounter at some point with their furnaces. Sometimes it’s human error. There’s a setting on most thermostats to set “continuous fan”. This will keep the fan running regardless of your heating or cooling settings. 

If human error is ruled out, it could be a sign of a faulty limit control switch. Try resetting the limit control switch before looking for a replacement part. 

Replacement Parts

Issue: Noisy Furnace or Duct Work

If you are hearing various noises from your furnace as it runs the sounds could indicate a mechanical issue, airflow problems, or a clogged burner. Sounds like rumbles, squeaks, or rattles aren’t normal for a furnace. If it sounds like the noise is related to air running through the ductwork, try insulating the ducts to cut down on the noise. 

Addressing the furnace noises could be as simple as replacing the pilot light or lubricating the blower motor ports. Don’t rule out the possibility of a belt or burner issue. 

If you’re hearing a popping sound, that could just be the ductwork expanding and contracting with the change of temperature. Rattling usually indicates something loose in the system that needs tightening. The big red flag is any grinding sounds in the system. Call a furnace expert as soon as possible, it could be a sign of motor issues.

Replacement Parts

Issue: Flame Sensor Needs Cleaning

The job of the flame sensor is extremely important. It’s the safeguard protecting your equipment and home from unsafe amounts of fuel being burnt. If the sensor is dirty or broken, it could cause your furnace to improperly function, or even worse, cause a fire in your home. 

The flame sensor can be found near the back side of the furnace. Make sure you turn off the furnace at the breaker box before starting. If possible, remove the sensor from the furnace and gently remove any dust or residue. Once you’ve finished cleaning, reattach the sensor and turn the power back on. 

If the sensor is broken, you can find a great range of replacement flame sensors by brands you trust like Supco, Packard, and White-Rodgers here at Jackson Systems & Supply.

Replacement Parts

These simple annual inspections can save you time and money down the road. As always be weary of DIY repairs that are outside of your comfort zone. Always call a service professional in those scenarios to avoid further damage to your equipment. 

The tips do not help solves issues above your skill level. A simple tune-up could cover most of these issues. The main goal is always to keep your furnace safe and running smoothly for the long winter months.

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