Furnace Won’t Start: Emergency Troubleshooting Guide

It’s freezing outside, your family is bundled up in blankets, and your furnace won’t turn on.

There’s no worse feeling than waking up to a cold house in the middle of January. You check the thermostat—it’s set to heat. You listen for the furnace—nothing. No click, no hum, no warm air coming from the vents. Your family is shivering, the pipes could freeze, and you don’t know if this is something simple or a full-blown emergency. At H&H Heating and Air Conditioning, we’ve helped thousands of Richmond families through exactly this moment. Before you panic—and before you spend a freezing night waiting for help—let us walk you through some things you can check yourself.

Check the Thermostat First

Thermostat issues cause a surprising number of “furnace won’t start” calls. Before assuming the worst, verify these basics: Is the thermostat set to HEAT (not cool or off)? Is the temperature set higher than the current room temperature? Is the display on?

Common thermostat mistakes: The most frequent issue is someone accidentally bumping the switch to “off” or “cool.” If your thermostat is battery-powered, dead batteries will prevent it from communicating with the furnace—the display may look fine but the signal isn’t getting through. Try setting the temperature 5 degrees higher than the current room temp to trigger the furnace.

Signs of thermostat malfunction: If the display is blank, unresponsive, or shows erratic readings, the thermostat itself may have failed. Try replacing the batteries first. If it’s hardwired and unresponsive, you may have a wiring issue or a failed unit.

Check the Power Supply

Even gas furnaces need electricity to run—the blower, ignition system, and controls all require power. A tripped breaker is one of the most common reasons a furnace won’t start.

What to check: Find your electrical panel and look for the furnace breaker. If it’s tripped (sitting in the middle position), flip it fully OFF, then back ON. Also locate the furnace power switch—it looks like a light switch and is usually on the furnace itself or on a nearby wall. It’s easy for someone to accidentally flip it off thinking it’s a light.

If the breaker trips again immediately: Don’t force it back on. This indicates an electrical short that requires professional diagnosis—continuing to reset it could cause damage or create a fire hazard.

Check the Air Filter

A severely clogged filter can actually shut down your furnace completely. When the filter restricts airflow, the heat exchanger overheats, and the limit switch trips as a safety precaution.

What happens inside: Without adequate airflow, heat builds up inside the furnace. The limit switch detects the dangerous temperature and shuts everything down to prevent damage or fire. This is your furnace protecting itself.

During Virginia winters, check your filter monthly. Hold it up to light—if you can’t see through it, replace it. A clogged filter is one of the easiest problems to prevent and one of the most common causes of furnace shutdown.

Checked all the basics and still no heat? Call H&H—we offer 24/7 emergency service.

Check the Pilot Light or Ignition

Older furnaces have a standing pilot light—a small flame that burns continuously. If it goes out (from a draft, thermocouple issue, or gas interruption), the furnace won’t ignite. Look through the small window on the furnace. If you don’t see a small blue flame, the pilot is out. Most furnaces have relighting instructions on a label inside the access panel.

Modern furnaces use electronic ignition—there’s no standing pilot to check. Signs of ignition failure include hearing clicking sounds (the igniter trying to spark) but no flame igniting, or the furnace starting briefly then shutting down within seconds.

Important: If you smell gas, do NOT attempt to relight anything. Leave the house immediately and call your gas company.

Gas Supply Issues

Your furnace needs fuel. If the gas supply is interrupted, nothing will ignite.

How to check: The gas valve near your furnace has a handle. When the handle is parallel to the pipe, gas is flowing. When it’s perpendicular (crossways), the gas is off. Also check if other gas appliances in your home work—try your stove or water heater. If nothing gas-powered is working, contact your gas company.

If you smell gas: This is an emergency. Don’t flip any switches, don’t use your phone inside, don’t do anything that could create a spark. Get everyone out of the house and call 911 from outside.

Safety Switches That Stop Your Furnace

Modern furnaces have multiple safety switches designed to shut down the system if something dangerous is detected. If any of these trips, your furnace won’t run.

Limit switch: Shuts down the burner if the furnace overheats—often caused by a dirty filter or blocked vents.

Pressure switch: Ensures the combustion chamber is properly vented before allowing ignition. If the inducer motor isn’t creating proper airflow, this switch prevents startup.

Flame sensor: Detects whether the burner is actually lit. If no flame is detected within seconds of the gas valve opening, it shuts everything down to prevent gas buildup.

Rollout switch: Trips if flames escape the combustion chamber—a serious condition that could indicate a cracked heat exchanger or blocked flue.

Any tripped safety switch means something triggered it. While some (like the limit switch) may reset automatically once the furnace cools, others require manual reset. If a safety switch trips repeatedly, call a professional—there’s an underlying problem that needs diagnosis.

Blower Motor and Electrical Issues

If your furnace ignites but no air comes out of your vents, the blower motor may have failed.

Signs of blower motor problems: You hear the furnace fire up, but no air flows through the vents. Or you hear a humming sound but the fan doesn’t spin.

What humming without spinning means: This usually indicates a failed capacitor—the component that stores extra electricity to kick-start the heavy blower motor. Capacitors are relatively inexpensive to replace, but the diagnosis and repair require a technician.

How serious is it? A failed capacitor is a moderate repair. A failed blower motor is more expensive but still repairable. Either way, you need professional diagnosis.

When to Call for Emergency Service

Stop troubleshooting and call immediately if:

• You smell gas (evacuate first, then call)
• You’ve tried the basic steps and nothing worked
• The furnace starts but shuts off within seconds or minutes
• You hear strange noises, smell burning, or see visible damage
• Your house is getting dangerously cold
• You have vulnerable family members—elderly, infants, or anyone with medical conditions

How quickly can it become dangerous? In freezing weather, an unheated home can drop below 50°F within hours. Pipes can begin freezing when temperatures stay below 32°F for extended periods. If you have vulnerable family members, don’t wait—call for emergency service.

What to Do While Waiting for Help

Use space heaters safely. Keep them at least three feet from anything flammable. Never leave them unattended. Plug directly into wall outlets, not extension cords.

Conserve heat. Close off unused rooms. Gather the family in one room with blankets. Close blinds and curtains to add insulation.

Protect your pipes. Open cabinet doors under sinks on exterior walls. Let faucets drip slightly to keep water moving.

Don’t use your oven or stovetop for heat. Gas appliances produce carbon monoxide, and using them for heating creates a serious poisoning risk.

How H&H Handles Emergency Furnace Calls

When you call H&H for an emergency, you get fast response from local technicians who know Richmond and Goochland. Our trucks are stocked with common parts so many repairs can be completed the same visit.

We diagnose before recommending repairs—we’re not going to sell you parts you don’t need. We give upfront pricing even on emergency calls. And if your system needs replacement rather than repair, we’ll tell you honestly and explain why.

Keep Your Family Warm

A furnace that won’t start is stressful, but it’s not always a catastrophe. Sometimes it’s a tripped breaker, a clogged filter, or a thermostat issue you can fix in minutes. Other times, it’s a sign of something more serious that needs professional attention.

At H&H Heating and Air Conditioning, we’re available 24/7 for heating emergencies. When you call, you’ll get fast response, honest diagnosis, and no pressure—just solutions to get your family warm again.

Furnace won’t start and you’ve tried everything? Call H&H now—we’re available 24/7 for emergency heating service in Richmond and Goochland.

Frequently Asked Questions