It's 28 degrees outside, the wind is howling off the Atlantic, and your furnace just stopped working. Before you panic and before you spend $150+ on an emergency HVAC call — check these 8 things first. Several of them take less than two minutes and could save you hundreds of dollars.
About 25–30% of “furnace not working” service calls turn out to be something the homeowner could have fixed themselves. We'll walk you through each check, tell you exactly what to look for, show you the DIY fix when there is one, and be straight with you about when it's time to call a licensed HVAC technician.
1. Check Your Thermostat Settings
Time to check: 30 seconds
This is the number one thing HVAC technicians find on “no heat” service calls. It sounds too simple, but it happens constantly — especially in households where multiple people adjust the thermostat.
What to look for:
- Is it set to HEAT? Someone may have bumped it to COOL, FAN ONLY, or OFF. Check the mode setting first.
- Is the set temperature higher than the current room temperature? If your thermostat reads 68°F and it's set to 66°F, the furnace won't kick on. Bump it up 5 degrees above the current room temp to test.
- Are the batteries dead? Many thermostats run on AA or AAA batteries. If the screen is blank, dim, or flickering, replace the batteries. A thermostat with dead batteries can't send a signal to start the furnace.
- Is the thermostat programmed to a schedule? Programmable and smart thermostats may have switched to a “sleep” or “away” mode with a lower set point. Check the schedule and override it.
- Did someone accidentally hit a lockout or hold? Some Honeywell and Ecobee thermostats have a “hold” feature that overrides the schedule at a fixed temperature. Clear any holds.
DIY fix:
Set the thermostat to HEAT, bump the temperature 5 degrees above the current room temp, and wait 3–5 minutes. If the furnace fires up, you're done. Replace batteries if the screen was dim.
When you need a pro:
If the thermostat appears to be working (screen is on, settings are correct) but the furnace doesn't respond at all, the issue is likely with the furnace itself or the wiring between the thermostat and furnace. Move on to check #2.
2. Check and Replace Your Air Filter
Time to check: 5 minutes
A clogged air filter is the single most common cause of furnace problems, and it leads to cascading failures if left unchecked. When the filter is packed with dust, pet hair, and debris, it chokes off airflow to the furnace. The furnace overheats internally, and the high-limit safety switch shuts it down to prevent a fire.
What to look for:
- Pull the filter out (usually located where the return duct meets the furnace, or in a slot on the side/bottom of the air handler).
- Hold it up to light. If you can't see light through it, it's too dirty.
- A dark gray or black filter that's stiff with compacted debris is well past due.
DIY fix:
Replace the filter with a new one. Standard 1-inch filters cost $5–$15 at any hardware store — match the size printed on the filter frame. If you don't have a replacement, you can run the furnace without a filter temporarily (a few hours) while you get a new one. It's not ideal, but it's better than no heat in a NJ winter.
After replacing the filter, wait 15–30 minutes. The furnace's high-limit switch needs time to cool down and reset. Then set the thermostat to call for heat. If the furnace fires up, your clogged filter was the problem.
When you need a pro:
If the furnace has been running with a severely clogged filter for a long time, the heat exchanger may have been stressed by repeated overheating. If the furnace starts short-cycling (running for a few minutes, shutting off, running again) even with a clean filter, a technician should inspect the heat exchanger and high-limit switch. A cracked heat exchanger is a serious safety issue because it can leak carbon monoxide.
3. Check the Circuit Breaker
Time to check: 2 minutes
Even gas furnaces need electricity to operate. The blower motor, ignition system, control board, and thermostat circuit all run on electrical power. If the furnace's breaker tripped, nothing will work.
What to look for:
- Go to your electrical panel (breaker box).
- Find the breaker labeled “Furnace,” “HVAC,” or “Air Handler.” There may be two breakers if you have both a furnace and an AC condenser.
- If the breaker is in the middle position (not fully ON and not fully OFF), it has tripped.
- Also check: some furnaces have a power switch that looks like a regular light switch, usually mounted on or near the furnace. Make sure it's ON. These get accidentally turned off during laundry, cleaning, or storage activity near the furnace.
DIY fix:
Flip the tripped breaker fully OFF, wait 30 seconds, then flip it back ON. If the furnace starts up and runs normally, a power surge likely tripped the breaker. NJ winter storms frequently cause momentary power interruptions that trip furnace breakers.
When you need a pro:
If the breaker trips again within minutes of resetting it, do not keep resetting it. A repeatedly tripping breaker means there's a short circuit or ground fault in the furnace's electrical system — possibly a failing blower motor, a wiring issue, or a bad control board. An HVAC technician should diagnose this. Expect $150 – $400 for electrical diagnosis and repair.
4. Check the Gas Supply
Time to check: 2 minutes
If you have a gas furnace (most NJ homes with forced-air heating do), the gas supply can get interrupted without you realizing it.
What to look for:
- Gas valve at the furnace: There's a manual shutoff valve on the gas line leading to the furnace. The handle should be parallel (in line) with the pipe — that means open. If it's perpendicular (crosswise), the gas is shut off.
- Other gas appliances working? Turn on a gas stove burner or check the water heater pilot. If nothing gas-powered is working, the issue is your main gas supply, not just the furnace.
- Smell gas? If you smell rotten eggs (the odorant added to natural gas), leave the house immediately, don't flip any switches, and call PSE&G (or your gas utility) from outside. This is a gas leak emergency.
DIY fix:
If the gas valve was accidentally turned off, turn it back on (handle parallel to pipe). Wait 5 minutes for gas to reach the furnace, then set the thermostat to call for heat. If the furnace fires up, you're done.
When you need a pro:
If the gas valve is open, other gas appliances work, but the furnace still won't ignite, the issue is likely with the furnace's gas valve, ignition system, or flame sensor. These are not DIY repairs. An HVAC technician should handle anything involving the furnace's internal gas components.
5. Check the Pilot Light or Igniter
Time to check: 5–10 minutes
How your furnace lights depends on its age and type:
Standing pilot light (older furnaces, pre-2000):
Older furnaces have a small flame that burns continuously. If this pilot light goes out, the furnace can't ignite the burners.
- Open the furnace access panel (usually the lower panel).
- Look for the pilot light — a small blue flame near the bottom of the burner assembly.
- If it's out, follow the relighting instructions printed on the furnace (typically: turn gas valve to PILOT, hold the reset button, light the pilot with a long lighter, hold for 30 seconds, then release).
Electronic ignition (most furnaces after 2000):
Modern furnaces use either a hot surface igniter (a glowing element, like a car cigarette lighter) or a spark igniter. These are visible through the furnace's viewing window (a small glass porthole on the front panel).
- Set the thermostat to call for heat and watch through the viewing window.
- You should see the igniter glow orange/red or hear a clicking spark within 30–60 seconds of the inducer fan starting.
- If the igniter glows but the burners don't light, the issue may be a dirty flame sensor (see below).
- If the igniter doesn't glow or spark at all, it's likely burned out.
DIY fix (pilot light only):
You can safely relight a standing pilot light by following the furnace manufacturer's instructions. If the pilot won't stay lit after several attempts, the thermocouple (a safety sensor near the pilot) may need replacing — this is a $15 part but should be replaced by a technician.
When you need a pro:
Hot surface igniters and spark igniters are replaceable parts ($80 – $250 installed), but they require opening the furnace and working around the gas system. A dirty flame sensor is one of the most common furnace failures and is usually a $80 – $150 service call to clean or replace. Some handy homeowners clean flame sensors themselves (fine sandpaper or steel wool on the sensor rod), but if you're not comfortable, call a tech.
6. Check the Blower Motor
Time to check: 2 minutes
The blower motor is the fan that pushes heated air through your ductwork and into your rooms. If the furnace fires up (you can hear the burners ignite) but no warm air comes out of your vents, the blower motor may be the issue.
What to look for:
- Set the thermostat fan setting to ON (not AUTO). This tells the blower to run continuously regardless of whether the furnace is heating.
- Go to a supply vent. Do you feel air moving?
- Listen near the furnace. Do you hear the blower fan running, or is it silent? A humming sound without the fan spinning could mean a seized motor or a bad capacitor.
DIY fix:
There's no true DIY fix for a failed blower motor, but you can check one thing: the blower access panel. Most furnaces have a safety switch on the blower compartment door — if the door isn't fully closed, this switch prevents the blower from running. Push the door firmly until it clicks into place.
When you need a pro:
A failing blower motor, a bad motor capacitor, or a burned-out blower relay all require a technician. Blower motor replacement typically costs $300 – $600 for the motor, or $100 – $250 if it's just a bad run capacitor. Capacitor replacement is one of the most cost-effective furnace repairs and takes about 30 minutes.
7. Check for Blocked Vents and Registers
Time to check: 10 minutes
If the furnace is running but your house isn't getting warm, the problem might not be the furnace at all — it might be blocked airflow in your ductwork or vents.
What to look for:
- Closed supply vents: Walk through every room and make sure all supply vents (the ones that blow air) are fully open. People close vents in unused rooms, which restricts total system airflow and can cause the furnace to overheat and shut down.
- Blocked return vents: Return air grilles (the larger ones that pull air back to the furnace) must not be blocked by furniture, curtains, or rugs. A blocked return starves the furnace of airflow.
- Dirty registers: Thick dust buildup on vent covers restricts airflow. Vacuum them or wipe them down.
- Ice or debris on the exhaust vent: High-efficiency furnaces vent through PVC pipes that exit through the side of the house. In NJ winters, ice, snow, or debris can block the exhaust or intake pipe. Go outside and check that both PVC pipes are clear and unobstructed. This is a common and overlooked cause of furnace shutdowns during heavy snow.
DIY fix:
Open all vents, clear all obstructions, clean dirty registers, and clear any ice or snow from exterior exhaust and intake pipes. After clearing obstructions, wait a few minutes and see if the furnace resumes normal operation.
When you need a pro:
If all vents are open and clear but airflow is still weak throughout the house, you may have a ductwork problem — collapsed flex duct, disconnected joints, or excessive buildup inside the ducts. Duct inspection and repair typically costs $200 – $500. Full duct cleaning runs $300 – $600 for a typical NJ home.
8. Check the Condensate Drain (High-Efficiency Furnaces)
Time to check: 5 minutes
If you have a high-efficiency condensing furnace (90% AFUE or higher — you can tell because it vents through white PVC pipes instead of a metal flue), it produces condensation as a byproduct of combustion. This water drains through a small tube or hose, usually into a floor drain, utility sink, or condensate pump.
What to look for:
- Find the condensate drain line. It's usually a small-diameter plastic tube coming out of the bottom or side of the furnace.
- Is water pooled around the base of the furnace? That could indicate a clogged drain.
- If you have a condensate pump, is the pump working? Check that it has power and isn't overflowing.
- Is the drain line frozen? In unheated spaces (crawl spaces, uninsulated areas), the condensate line can freeze in NJ winters, backing up into the furnace and triggering a safety shutdown.
DIY fix:
If the drain line appears clogged, you can try clearing it by disconnecting the line at the furnace end and blowing through it (or using a wet/dry vacuum on the other end). If the condensate pump isn't running, check that it's plugged in and that the float switch isn't stuck. For a frozen condensate line, thaw it with warm (not boiling) water.
When you need a pro:
If clearing the drain doesn't resolve the issue, or if the furnace continues to shut down and produce error codes related to pressure or drainage, a technician should inspect the condensate trap, drain system, and secondary heat exchanger. Condensate system repairs typically cost $100 – $300.
Common Furnace Problems by Type
Different furnace types have different failure patterns. Here's what to expect based on what you have:
Gas Furnace (Most Common in NJ)
Gas furnaces are the standard in most New Jersey homes, and they're generally reliable. The most common failures are:
- Dirty flame sensor: The #1 service call. Furnace lights, runs for a few seconds, then shuts off. The flame sensor can't detect the flame and kills the gas for safety. Cost to fix: $80 – $150.
- Failed igniter: Furnace won't light at all. The hot surface igniter cracks or burns out after 5–7 years. Cost to fix: $100 – $250.
- Bad gas valve: Gas doesn't flow to the burners even though the igniter is working. Cost to fix: $200 – $600.
- Cracked heat exchanger: The most serious (and expensive) issue. Can leak carbon monoxide. Often means replacement is more economical than repair. Repair cost: $500 – $1,500. If the unit is over 15 years old, replacement is usually recommended.
- Draft inducer motor failure: The motor that pulls combustion gases through the heat exchanger fails. Furnace won't start or shuts down with a pressure switch error. Cost to fix: $200 – $600.
Electric Furnace
Electric furnaces are less common in NJ (they're expensive to operate given our electricity rates) but some homes have them, especially condos and apartments.
- Failed heating element: Electric furnaces have multiple heating elements (like large toaster coils). If one fails, you get reduced heating. If multiple fail, you get no heat. Cost per element: $100 – $300 installed.
- Tripped high-limit switch: Usually caused by a clogged filter or blocked airflow. Reset by replacing the filter and pressing the reset button (if there is one).
- Sequencer failure: The sequencer stages the heating elements to avoid turning them all on at once (which would draw too many amps). A bad sequencer causes intermittent heating. Cost to fix: $150 – $350.
- Breaker issues: Electric furnaces draw significant amperage. Loose breaker connections or undersized wiring cause intermittent shutdowns.
Heat Pump (Heating Mode)
Heat pumps are growing in NJ thanks to energy efficiency incentives, but they operate differently from traditional furnaces in heating mode.
- Defrost cycle problems: In heating mode, the outdoor coil can ice up. The system should defrost automatically. If the defrost control board or defrost sensor fails, ice builds up and heating capacity drops dramatically. Cost to fix: $200 – $500.
- Reversing valve stuck: The reversing valve switches the heat pump between heating and cooling. If it sticks in cooling mode, you'll get cold air in winter. Cost to fix: $300 – $700.
- Low refrigerant: Unlike gas furnaces, heat pumps use refrigerant to transfer heat. A leak reduces heating capacity, especially in cold weather when the system is already working hard. Cost to find and fix leak + recharge: $300 – $800.
- Auxiliary heat not engaging: When outdoor temps drop below 35–40°F, the heat pump relies on backup electric heat strips (aux heat). If these fail, you'll notice a sharp drop in comfort on the coldest NJ days. Cost to fix: $100 – $300 per strip.
Emergency: No Heat in a NJ Winter — What to Do Right Now
If it's below freezing outside, your furnace is dead, and you can't fix it with the checks above, here's your immediate action plan to stay safe and prevent damage to your home:
Stay warm safely
- Use portable space heaters carefully. Place them on flat, hard surfaces, at least 3 feet from anything flammable (curtains, furniture, bedding). Never leave them unattended or running overnight. Choose electric heaters with tip-over safety switches and auto-shutoff.
- Never use your oven or gas stove for heat. Gas ovens produce carbon monoxide. Electric ovens are a fire hazard when left open for extended periods. This kills people every NJ winter — it is never safe.
- Never use a generator indoors or in an attached garage. Carbon monoxide from generators is lethal. Generators go outside, at least 20 feet from any window or door.
- Close off unused rooms. Concentrate your heat sources (space heaters) in the rooms where people are sleeping and living. Close doors to unused rooms to reduce the space you need to heat.
- Layer up. Blankets, sleeping bags, winter coats. If you have small children or elderly family members, this is especially critical — they lose body heat faster.
Prevent frozen pipes
This is the most expensive risk when your heat goes out in a NJ winter. A burst pipe from freezing can cause $5,000–$50,000+ in water damage. Take these steps immediately:
- Open cabinet doors under sinks on exterior walls to let warmer room air reach the pipes.
- Let faucets drip. A slow, steady drip from both hot and cold lines on exterior walls keeps water moving and reduces freeze risk. Focus on the kitchen sink, bathroom sinks on outside walls, and any pipes in unheated spaces.
- If you have a basement, keep it above 55°F if possible. This is where most of your plumbing runs. A space heater in the basement can prevent thousands in pipe damage.
- Know where your main water shutoff is. If a pipe does burst, shutting off the water supply immediately limits the damage. In most NJ homes, the main shutoff is near where the water line enters the house (often in the basement near the front wall).
When to call emergency HVAC
Call for emergency service if:
- Your home has dropped below 55°F and is still falling
- You have elderly residents, infants, or anyone with medical conditions sensitive to cold
- You smell gas near the furnace (call the gas company first: PSE&G emergency line is 1-800-880-7734)
- The furnace is making unusual sounds (banging, screeching, grinding) before shutting down
- You've tried all 8 checks above and nothing works
Emergency HVAC calls in NJ typically cost $150 – $300 for the service call alone, plus parts and repair. After-hours rates (evenings, weekends, holidays) are usually 1.5x–2x the regular rate. It's expensive, but it's far cheaper than frozen pipes and water damage.
Cost of Common Furnace Repairs in NJ
Here's what you can expect to pay for the most common furnace repairs in the NJ market:
- Diagnostic service call: $80 – $150 (this is just to show up and diagnose; many companies apply this toward the repair cost)
- Flame sensor cleaning/replacement: $80 – $200
- Igniter replacement: $100 – $250
- Thermocouple replacement: $100 – $200
- Blower motor capacitor: $100 – $250
- Draft inducer motor: $200 – $600
- Blower motor replacement: $300 – $600
- Gas valve replacement: $200 – $600
- Control board replacement: $300 – $700
- Heat exchanger replacement: $500 – $1,500
- Complete furnace replacement: $3,000 – $7,000 (standard efficiency) to $5,000 – $10,000 (high-efficiency)
The general rule: if a single repair costs more than 50% of a new furnace AND your furnace is over 15 years old, replacement usually makes more financial sense.
Signs You Need a New Furnace vs. a Repair
Not every breakdown means you need a new furnace. But sometimes repair is throwing good money after bad. Here's how to tell the difference:
Repair makes sense when:
- The furnace is under 12 years old
- The issue is a single component (igniter, flame sensor, capacitor, thermostat)
- Repair cost is under $500
- The furnace has been well-maintained (annual tune-ups, regular filter changes)
- This is the first major repair
Replacement makes sense when:
- The furnace is 15–20+ years old
- The heat exchanger is cracked (safety issue + expensive repair on an aging system)
- Repair cost exceeds 50% of a new furnace
- You've had multiple repairs in the past 2–3 years (the “nickel and dime” pattern)
- Your energy bills have been climbing steadily despite maintenance (the furnace is losing efficiency as it ages)
- The furnace is a low-efficiency model (80% AFUE) and you want to upgrade to high-efficiency (95–98% AFUE) — you'll save 15–20% on heating costs
- The furnace uses R-22 refrigerant (for heat pump systems) which is no longer manufactured and extremely expensive
NJ winter urgency:
Don't wait until a polar vortex hits to find out your furnace is on its last legs. NJ HVAC companies get slammed with emergency calls during cold snaps, which means longer wait times and higher prices. If your furnace is over 15 years old and acting up, get it inspected in the fall when technicians are less busy and you have time to plan a replacement if needed.
Frequently Asked Questions
Why does my furnace keep turning on and off every few minutes?
This is called short-cycling. The most common causes are: a clogged air filter (check that first), a dirty flame sensor (furnace lights, runs 3–10 seconds, shuts off), an overheating heat exchanger triggering the high-limit switch, or a thermostat malfunction. Start with the filter. If that doesn't fix it, call a technician to check the flame sensor and heat exchanger.
My furnace is blowing cold air. What's wrong?
If the fan is blowing but the air isn't warm: first check if the thermostat fan is set to ON instead of AUTO (ON runs the fan even when the furnace isn't heating). If it's set to AUTO and the air is still cold, the burners aren't firing — could be a bad igniter, flame sensor, gas supply issue, or a tripped safety switch. Also check if the pilot light is out (older furnaces).
Is it safe to run my furnace if it smells like burning?
A brief burning smell when the furnace first starts for the season is normal — it's dust burning off the heat exchanger and burners. It should go away within 30–60 minutes. If the burning smell persists, is strong, or smells like plastic or electrical burning, shut the furnace off and call a technician. A persistent burning smell can indicate an overheating motor, a wiring issue, or a cracked heat exchanger.
How often should I have my furnace serviced?
Once a year, ideally in the fall before the heating season starts. Annual maintenance includes cleaning the burners and flame sensor, checking the heat exchanger for cracks, testing safety controls, lubricating moving parts, and checking gas pressure. Cost: $80–$150 for a tune-up. Many NJ HVAC companies offer maintenance plans at $150–$250/year that include one furnace tune-up and one AC tune-up plus discounts on repairs.
What does the blinking light on my furnace mean?
Most modern furnaces have a diagnostic LED on the control board, visible through the lower access panel or viewing window. The light blinks a code — for example, 3 blinks might mean “pressure switch stuck open” and 4 blinks might mean “high-limit switch open.” The code chart is printed on a sticker inside the furnace access panel or in your owner's manual. Write down the blink pattern and tell your HVAC technician — it speeds up diagnosis significantly.
Can a dirty filter actually damage my furnace?
Yes. A severely clogged filter restricts airflow so badly that the heat exchanger overheats repeatedly. Over time, this thermal stress can crack the heat exchanger, which is a $500–$1,500 repair (or more often, a reason to replace the entire furnace). A $10 filter every 1–3 months prevents a potentially catastrophic failure. It's the single best thing you can do for your furnace.
My furnace works but my house is still cold. Why?
If the furnace is running and producing heat but your house isn't reaching the set temperature, the problem is usually outside the furnace: poor insulation (very common in older NJ homes), leaky windows and doors, ductwork leaks (losing heated air in unconditioned spaces like attics and crawl spaces), or an undersized furnace for the home's square footage. Start by checking for drafts around windows and doors, and make sure all vents are open and unobstructed.
How long does a furnace last in NJ?
Gas furnaces last 15–25 years on average, with 20 years being a common lifespan for well-maintained units in NJ. Electric furnaces can last 20–30 years because they have fewer moving parts and no combustion components. Heat pumps used for heating typically last 12–17 years. NJ's cold winters mean furnaces run hard for 4–5 months a year, which is more wear than milder climates. Annual maintenance extends lifespan; neglected furnaces tend to fail around the 12–15 year mark.
Don't Wait Until You're Freezing
A furnace breakdown in a NJ winter is more than an inconvenience — it's a risk to your family's comfort and your home's plumbing. If you've gone through all 8 checks above and your furnace still isn't working, MainStreet Service Pros connects you with licensed, insured HVAC technicians in Elizabeth, NJ and across Union County. Fast response, transparent pricing, no high-pressure sales. Get your heat back on.