No matter where you live, a functional heating system is essential for comfort during chilly winter weather. A furnace not working is a frustrating and potentially dangerous issue, so you need a prompt diagnosis and repair. That’s why we’re here to explain several common reasons why furnaces fail. With this knowledge, you’ll know when to resolve a problem yourself or call an HVAC repair company.
1. Thermostat Issues
If your heating system fails to operate, start by checking your thermostat. If the display is blank, your thermostat may only need new batteries. If you cannot find your thermostat’s user manual, check the manufacturer’s website for a PDF version.
Some thermostats have a fabric strap to help you extract their batteries. After installing new batteries, carefully position this strap before reattaching the thermostat to the wall bracket. A misaligned battery strap can cover the electrical contacts necessary for your furnace and air conditioner.
With a functional display panel, make certain that the thermostat is set for “Heat,” not “A/C” or “Off.” If your thermostat displays an error code, check your thermostat’s manual to see if the issue is one you can resolve yourself.
If these steps fall short, contact an HVAC service professional.
2. Clogged Filters
Some furnace difficulties simply come down to a dirty filter. Clogged filters can lead to inadequate heat from your vents and lower air quality. Extremely dirty filters may trigger rapid combustion cycling, shortening your furnace’s service life.
Replacing the filter is easy to do yourself. Check your furnace’s manual for the correct filter type for your unit, and follow your furnace manufacturer’s filter replacement schedule.
Adding filter replacement dates to your smartphone’s calendar app can head off furnace problems and boost home air quality. If family members suffer from dust allergies, it’s okay to replace filters more often than the manufacturer’s recommendation.
3. Igniter Failure
With a properly functioning furnace, you will hear a click moments after setting your thermostat above room temperature. That telltale sound signals the beginning of the combustion process that supplies warm air.
Furnace igniters are the safer and more energy-efficient successors of older pilot lights. Before your furnace releases gas for combustion, electricity warms the igniter’s heating element to a temperature that may reach 2,500 degrees Fahrenheit.
When gas flows across the igniter, combustion begins and continues until the gas valve closes. Once combustion commences, the igniter shuts down within a minute.
Why Igniters Fail
When an igniter fails, the furnace’s control board aborts the remaining combustion cycle. Age is a primary cause of igniter failures. With a well-maintained furnace, an igniter will last at least five years.
Eventually, heat cycles take their toll and the igniter element fails. A malfunctioning furnace gas valve can accelerate igniter failure. Rapid on-off combustion cycling can also shorten your igniter’s life. A clogged air filter, blocked vents, or an issue with the furnace’s blower fan can trigger these short cycles.
An HVAC professional can also fix other igniter difficulties. Igniter heating elements are often fragile, making installation a delicate task. Touching the heating element with a bare finger passes on skin oil, shortening the component’s service life, so always call an expert to inspect your unit instead of attempting DIY repair.
4. Gas Valve Issues
Your furnace not working may stem from a malfunctioning gas valve. Without natural gas flow, no combustion begins, and no heating happens. Your furnace’s gas valve begins and ends that gas flow.
Naturally, no combustion occurs if the valve assembly sticks in the off position. Stuck valves are not the sole problem with these valves. Excessive flow rates can shorten an igniter’s lifespan.
If you set your thermostat higher and don’t hear combustion begin after the igniter sound, you may have a faulty valve. Furnace valve issues require a certified technician for resolution, so call in a professional for this task.
Natural Gas Leaks
Numerous safety features in modern furnaces prevent malfunctioning gas valves from leaking natural gas into your home. Nevertheless, gas leaks occur in rare circumstances.
If you smell natural gas from the furnace, exit the house immediately. Leave at least one door open to vent the gas, and then call your utility’s emergency number.
5. Draft Inducer Motor Failure
Your furnace’s draft inducer motor runs for the duration of the heating cycle. Before ignition, the motor’s attached fan flushes any residual harmful gases outdoors through the furnace vent or chimney. After ignition, the fan supplies oxygen for combustion.
Over time, the inducer motor’s bearings or drive shaft may wear out, leading to failure. If you hear loud noises from your system immediately after setting the thermostat, you might have a failing inducer motor. Your furnace’s built-in safety mechanisms will prohibit ignition if the motor fails completely. Still, call a heating professional for repairs to avoid furnace downtime on a chilly day.
6. Blower Motor Failure
Most gas furnaces distribute heat with forced air systems. Forcing that air through ducts and vents requires a blower motor. These motors pull double duty throughout the year, as they also circulate air for the air conditioner during the cooling season.
As with the inducer motor, a blower motor’s bearings can wear out. A seized bearing will quickly cause the motor to overheat, and the furnace’s built-in safety systems will shut the entire system down. Unusual squeaks or grinding noises may signal the imminent failure of a blower motor.
Blower fans resemble exercise wheels for small pets. Dust may accumulate over the closely spaced fan blades, impairing air circulation.
Fan blades loaded with dust can also trigger overheating and a system shutdown. An annual fan cleaning from an HVAC technician can prevent the need for an expensive blower motor replacement.
7. Clogged Drainage Lines
High-efficiency furnaces generate large amounts of condensation—water—that the system must drain off. With most systems, a transparent tube runs from your furnace to your basement drain.
If a clog occurs, a sensor will shut down your furnace. You may see a pool of water under your furnace before the sensor kicks in.
A drainage system examination is part of an annual checkup, another compelling reason for this preventative maintenance.
8. Faulty Control Boards
A lot happens between the time you set your thermostat to a higher temperature and the rush of warm air from your vents. Initiating a successful heating cycle requires several components to work in a precisely timed order. Your furnace’s control board is in charge of that sequence.
The board also monitors several sensors throughout the furnace and—when necessary—will rapidly shut down the system to keep your home safe. With forced air systems, the board also works in coordination with your air conditioner. The control board also allows you to run the fan without operating the A/C or furnace.
The control board for your furnace resembles any printed circuit board: a brown or green panel with soldered relays, switches, and transistors. Numerous wires from sensors, furnace components, and the main power switch plug into the control board.
Symptoms and Failure Causes
Does your heating system shut down before reaching the temperature you set on your thermostat? Or does the furnace drive your home’s temperature above your setting? In either case, a control board failure could be the cause.
Faulty signals from the control board may cause some furnace components to run too long or shut down prematurely. Common causes for control board failure include:
- Soldered Connections: Heat cycles over several years may cause a solder connection to fail permanently or intermittently.
- Transistors: A one-time voltage spike can burn out a transistor.
- Switches: Electromechanical switches handle several control board tasks. The long intervals between heating seasons raise the chance of these switches sticking in the “Off” position.
Resoldering connections and replacing transistors and switches yourself is not feasible; the solution to control board failures is a replacement by a qualified technician.
9. Cracked Heat Exchangers
When combustion occurs in your furnace, the heat exchanger transfers heat from the flue gases to breathable air. The blower then distributes this warm air throughout your house.
If an obstruction occurs anywhere in the air circulation path—filter, ducts, or vents—the risk of a heat exchanger fracture markedly increases. An HVAC technician can repair some cracks, but regular filter changes and duct cleanings can prevent heat exchanger issues from ever occurring.
Call Oakland Park’s One-Stop HVAC Company
Annual checkups with our professionals here at Cool by Design can save you money in the long run. We also provide heat pump repair services to answer the question, “why is my furnace not working?” to restore heat to your home when you need it most.
As a locally owned business, we’ve earned over a hundred five-star reviews from homeowners and businesses of all sizes. For all your furnace installation and repair needs, call us at Cool by Design at (954) 900-1098.