4 of the Most Common Furnace Problems (and Their Solutions)

Updated October 2026. The four furnace problems homeowners call about most, with the checks to try first, rewritten with ENERGY STAR maintenance guidance and CDC carbon monoxide figures checked this month.

The most common furnace problems are no heat, a furnace that won’t turn on, unusual noise and a furnace that shuts off before the house warms up. As of October 2026, most start with one of four things you can check in 10 minutes: the thermostat setting, a clogged filter, a tripped breaker or the ignition. ENERGY STAR says to inspect the filter once a month.

Jump to: 🏠 No heat · ⏱️ Won’t turn on · 🤝 Noises · 🪜 Shuts off early · 📍 When to call a pro · ❓ FAQ

A furnace usually fails on the coldest night of the year, because that’s when it works hardest. The good news: a lot of “broken” furnaces aren’t broken. They’re set wrong, starved for air or cut off from power. Go through the checks below in order. If none of them fixes it, you’ll at least be able to tell the technician what you’ve ruled out.

Why is my furnace running but not producing heat?

Start at the thermostat. Make sure it’s on heat, not cool or off, and that the target is a few degrees above the room temperature. Then check the fan. If the fan setting on your thermostat is “on” instead of “auto”, the blower runs all the time and pushes room-temperature air through the vents between heating cycles. It feels like the furnace isn’t heating when it simply isn’t firing yet.

Next, the air filter. A clogged filter chokes airflow, so the heat exchanger overheats and the furnace may shut the burners down to protect itself. ENERGY STAR’s maintenance checklist says to inspect, clean or change filters once a month in a furnace, heat pump or central air system. Replace it more often with pets, smokers or renovation dust in the house. A typical 1-inch filter costs a few dollars and takes a minute to swap.

Last, the ignition. Older furnaces use a standing pilot light. If it’s out, the manufacturer’s label on the furnace door shows how to relight it. Newer furnaces use electronic ignition, a hot surface igniter or an intermittent pilot. If you hear clicking but the burners don’t light, or the pilot won’t stay lit, stop there and call a technician. The flame sensor or thermocouple may need cleaning or replacement, and gas parts are not a DIY job.

Why won’t my furnace turn on at all?

Check power first. A furnace is an electrical appliance even when it burns gas. Look in the breaker box for a tripped furnace breaker and reset it once. HVAC specialists at performancebasedheatingandair.com recommend opening the breaker box and flipping the furnace switch back on as one of the first checks. If it trips again right away, leave it off: that points to an electrical fault, and our guide on finding the right electrical services can help.

Then check the service switch. Most furnaces have a switch that looks like a light switch on the wall or the unit itself, and people flip it off by mistake. Make sure the front panel is closed tight too, since many furnaces have a safety switch that keeps them off when the door is loose.

Other common causes are a thermostat with dead batteries, a clogged filter, a faulty ignition and, with oil or propane, an empty tank. Work through them one at a time. If everything checks out and it still won’t start, the control board, inducer motor or a sensor may be at fault, and that needs a professional.

What do furnace noises mean?

Some hum and a soft whoosh when the burners light are normal. New or louder sounds usually mean something specific:

• Rattling or knocking: a loose panel, duct or screw, or a part of the blower that’s come loose.
• Squealing: a worn or slipping belt on older belt-driven blowers, or a motor bearing that needs attention.
• Booming or a loud bang at startup: delayed ignition, where gas builds up before it lights. Turn it off and call a technician.
• Scraping or grinding: metal on metal in the blower or motor. Shut it down right away.
• Rapid clicking without ignition: an igniter or gas valve problem.

You can tighten a loose access panel yourself. Anything inside the burner area, the blower housing or the gas line belongs to a pro. ENERGY STAR lists tightening electrical connections and lubricating moving parts as part of a contractor’s annual check-up, which is the best way to stop most noises before they start.

Why does my furnace shut off before the house is warm?

This is called short cycling. The furnace starts, runs a few minutes and stops, again and again. The usual suspects are a clogged filter, a dirty flame sensor, an oversized furnace or a thermostat placed near a heat source like a sunny window or a lamp.

Many furnaces also shut down when a safety device trips. The pressure switch is one example: it confirms the draft inducer is venting exhaust properly, and if the vent is blocked it shuts the furnace off. Learn more about the safety switch and why it trips. Check that the outside vent isn’t blocked by snow, leaves or a bird’s nest.

If the filter is clean, the vents are clear and it still short cycles, call a technician. Repeated cycling wears out parts faster and drives up the gas bill. Our guide to HVAC systems explains how furnaces, heat pumps and AC work together, and the same airflow rules apply to cooling; see cooling mistakes that can drain your finances.

When is a furnace problem a safety problem?

When you smell gas, see soot, or a CO alarm goes off. Leave the house and call the gas company or 911 from outside. CDC notes that gas- and oil-burning furnaces produce carbon monoxide, and that each year more than 100,000 people visit an emergency department for unintentional CO poisoning. Flu-like symptoms that ease when you leave the house are a warning sign.

ENERGY STAR’s checklist warns that a dirty burner or cracked heat exchanger makes a furnace run less safely, and improperly working gas connections are a fire hazard. NFPA lists heating equipment among the five leading causes of home fires. CDC recommends having your heating system, water heater and other fuel-burning appliances serviced by a qualified technician every year, and installing CO detectors near every sleeping area. Our post on home improvements that are important for your safety covers detectors in detail.

Schedule that service in early fall. ENERGY STAR notes contractors get busy once winter arrives, and suggests timing check-ups with the clock change. High-efficiency furnaces also drain condensate, so a plugged drain line can leak; our post on the common causes of plumbing problems you need to know covers drains and water heaters.

Selling a home with an older furnace? Inspectors check it, and it’s one of the most common repairs requested after a home inspection. A service record helps.

A Beycome flat fee MLS listing starts at $99, with $0 due to Beycome at closing, in 17 states and DC. Buying? Ask for the furnace’s age and service history, and look at the Beycome buyer program: no upfront fee, Beycome keeps 1% of the price (minimum $1,499) and credits the rest of the buyer-agent commission at closing, with lender approval. It’s open to every buyer on homes listed by other agents (the commission credit can’t apply where no buyer-agent commission is offered, like most FSBO homes, or on homes listed by Beycome sellers).

Furnace questions