Furnace Not Producing Heat? Here's What to Do

A furnace that won't heat is stressful — especially in winter. Follow these step-by-step troubleshooting tips, learn what common "no heat" repairs cost, and know when to call a pro.

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Common "No Heat" Repair Costs

Item	Low	High
Thermostat Replacement	$50	$400
Ignitor Replacement	$100	$400
Flame Sensor Cleaning/Replacement	$75	$300
Gas Valve Replacement	$200	$1,500
Control Board Replacement	$200	$600
Blower Motor Replacement	$300	$2,500
Draft Inducer Motor Replacement	$200	$1,500
Diagnostic/Service Call Fee	$75	$200
After-Hours Emergency Fee	$150	$400

Costs reflect national averages for 2025–2026. Emergency and after-hours service typically adds $75–$200 to the total. Many companies waive the diagnostic fee if you proceed with the repair.

Immediate Steps When Your Furnace Won't Heat

Before calling a technician, run through these checks. About 30% of "no heat" calls turn out to be simple issues the homeowner can resolve.

Step 1: Check Your Thermostat

Make sure it's set to "Heat" mode (not "Cool" or "Off")
Set the temperature at least 3 degrees above the current room temperature
Replace the batteries if the display is blank or dim
Try switching from "Auto" to "On" for the fan — if the blower runs but no heat comes out, the problem is with the furnace itself, not the thermostat

Step 2: Check the Air Filter

A severely clogged filter can cause the furnace to overheat and shut down via the high-limit switch. Pull out the filter and hold it up to a light. If you can't see light through it, replace it. This alone fixes the problem in many cases.

Step 3: Check the Circuit Breaker

The furnace has its own breaker in your electrical panel. If it's tripped, flip it off completely, wait 30 seconds, and flip it back on. If it trips again immediately, do not keep resetting it — there's an electrical problem that needs professional attention.

Also check the furnace power switch, which looks like a light switch and is usually located on or near the furnace. It may have been accidentally turned off.

Step 4: Check the Gas Supply (Gas Furnaces)

Verify the gas valve near the furnace is in the open position (handle parallel to the pipe)
Check if other gas appliances (stove, water heater) are working — if none are, the issue may be with your gas service, not the furnace
If you smell gas, do not flip any switches. Leave the house immediately and call your gas company from outside.

Step 5: Check the Condensate Drain (High-Efficiency Furnaces)

High-efficiency (90%+ AFUE) furnaces produce condensation that drains through a tube. If this tube is clogged or frozen, the furnace will shut down. Check for water pooling around the furnace base and clear any visible blockages in the drain line.

Safety First — Critical Warnings

A furnace that isn't working can create safety hazards beyond just being cold. Take these seriously.

Carbon Monoxide Risks

A malfunctioning furnace — especially one with a cracked heat exchanger — can produce carbon monoxide (CO), an odorless, colorless gas that can be lethal. If your CO detector alarms:

Get everyone out of the house immediately — including pets
Call 911 from outside
Do not re-enter until emergency services clear the home
Have the furnace professionally inspected before using it again

If you don't have CO detectors, install them on every level of your home. This is not optional if you have a gas or oil furnace.

When to Evacuate

Leave your home immediately if you notice:

Gas smell (rotten egg odor)
Carbon monoxide detector alarm
Electrical burning smell coming from the furnace
Visible sparks or flames outside the furnace cabinet

Protecting Pipes From Freezing

If your furnace is out and temperatures are below freezing:

Open cabinet doors under sinks on exterior walls
Let faucets drip slightly to keep water moving
If you'll be without heat for an extended period, consider draining your water system or hiring an emergency plumber to winterize
Keep interior doors open to allow any available heat to circulate

Temporary Heating Solutions

While waiting for a repair:

Space heaters: Use only UL-listed electric space heaters. Keep them at least 3 feet from anything flammable. Never leave them unattended or running while you sleep.
Fireplace: If you have a working fireplace, use it — but make sure the damper is open and the chimney is clear.
Never use your oven for heating. A gas oven produces carbon monoxide, and an electric oven is a fire hazard. This is dangerous and should never be done.
Layer up: Close off unused rooms, use heavy blankets, and gather the household into one room to conserve body heat.

When It's a DIY Fix vs. When to Call a Pro

You Can Likely Fix It Yourself

Clogged air filter — Replace it ($5–$30)
Tripped breaker — Reset it (free, but investigate if it trips again)
Thermostat batteries — Replace them ($3–$5)
Thermostat settings — Switch to Heat mode, raise temperature
Furnace power switch — Flip it back on
Pilot light out — Relight it following the instructions on your furnace (older models only)

Call a Professional

Furnace doesn't respond after you've checked all the basics
You smell gas or a burning electrical odor
CO detector alarms
Furnace starts and then shuts off repeatedly
You see error codes flashing on the furnace control board
Furnace makes loud banging, screeching, or grinding noises
You've already replaced the filter and reset the breaker with no improvement

Expect to pay $75–$200 for a diagnostic fee, plus the cost of parts and labor. After-hours or emergency calls add $75–$200 to the total. See our furnace repair cost guide for detailed pricing, or check whether emergency furnace repair is available in your area.

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Furnace Not Heating FAQ

Why is my furnace running but not producing heat?

The most common causes are a dirty air filter (restricts airflow and triggers safety shutoff), a faulty ignitor (burners won't light), or a dirty flame sensor (furnace lights briefly then shuts down). Check the filter first — if that's not the issue, call a technician. See our [common furnace problems](/furnace-repair/common-problems) guide for a full list.

How long can a house go without heat before pipes freeze?

Pipes can begin to freeze when indoor temperatures drop below 55 degrees F, which can happen within 4–6 hours in a poorly insulated home when outdoor temperatures are below 20 degrees F. In a well-insulated home, you may have 12–24 hours. Take preventive steps immediately — let faucets drip and open cabinet doors under sinks.

Is no heat an emergency?

It depends on conditions. If it's below freezing outside, you have elderly family members, infants, or medical equipment that requires a warm environment, it's an emergency. Most HVAC companies offer 24/7 emergency service with response times of 2–6 hours. Expect to pay a premium of $75–$200 for after-hours service.

Why does my furnace turn on then shut off after a few seconds?

This is almost always a dirty flame sensor. The sensor can't detect the flame, so the control board shuts down the gas valve as a safety measure. Cleaning or replacing the flame sensor ($75–$300) usually fixes it. A clogged filter or faulty pressure switch can also cause this behavior.

How much does an emergency furnace repair cost?

Emergency furnace repairs typically cost $150–$600 total, including the diagnostic fee, after-hours surcharge, and the repair itself. The most common emergency repairs — ignitor replacement, flame sensor cleaning, and gas valve repair — fall in this range. Major repairs like a blower motor can run higher.

Should I use a space heater while waiting for furnace repair?

Electric space heaters are a safe temporary option if used correctly. Keep them at least 3 feet from flammable materials, plug them directly into a wall outlet (not an extension cord), and never leave them unattended or running overnight. Never use a gas oven, grill, or any open-flame device for indoor heating.

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