It is 11 PM on a January night in Belleville. The temperature outside is 22°F. You hear a loud bang from the basement, and then silence — your furnace has stopped running. The house is already beginning to cool.
This scenario is more common than most homeowners expect, and how you respond in the first 30 minutes matters. This guide walks through the correct sequence of actions, including critical safety checks, when to call a professional, and how to protect your household while waiting for service.
Critical Safety Notice: If you smell gas, hear a hissing sound near your furnace or gas lines, or if your carbon monoxide detector activates, do not follow the steps below. Leave the building immediately without using any electrical switches, leave the door open as you exit, and call 911 from outside. Do not re-enter until emergency services have cleared the building.
Step 1: Assess for Immediate Safety Hazards (2 Minutes)
Before touching anything, take 60 seconds to assess for the two most serious hazards associated with furnace failure:
Natural gas leak: Natural gas has a distinctive sulfur (rotten egg) odor added by utility companies specifically to make leaks detectable. If you smell this odor anywhere in the home, evacuate immediately and call 911. Do not operate any electrical switches, including light switches, as electrical arcing can ignite gas.
Carbon monoxide: Carbon monoxide is colorless and odorless. Your only reliable warning is a functioning CO detector. Illinois law (430 ILCS 135) requires carbon monoxide alarms in all residential buildings with fuel-burning appliances. If your CO alarm is sounding, evacuate immediately and call 911. If you experience symptoms of CO poisoning — headache, dizziness, nausea, confusion — evacuate and call 911 even if your alarm is not sounding.
If neither hazard is present, proceed to the diagnostic steps below.
Step 2: Perform Basic Diagnostic Checks (5–10 Minutes)
Many furnace failures that appear serious have simple causes that a homeowner can safely check. Work through these in order before calling a technician:
Thermostat settings and batteries: Confirm the thermostat is set to "Heat" mode (not "Cool" or "Fan Only") and that the set temperature is above the current room temperature. Many digital thermostats use AA or AAA batteries that can fail without warning, causing the thermostat to lose its settings. Replace the batteries and observe whether the furnace restarts.
Circuit breaker: Locate your home's electrical panel and check the breaker labeled for the furnace or air handler. A tripped breaker will be in the middle position between "On" and "Off." Reset it once by switching it fully to "Off" and then back to "On." If it trips again immediately, do not reset it a second time — a breaker that trips repeatedly indicates an electrical fault that requires professional diagnosis.
Furnace power switch: Gas furnaces have a dedicated power switch, typically mounted on the wall near the furnace and resembling a standard light switch. Confirm it is in the "On" position. This switch is sometimes accidentally turned off during cleaning or storage activities near the furnace.
Air filter condition: A severely clogged air filter restricts airflow to the point where the furnace overheats and triggers the high-limit safety switch, shutting the system down. Locate the filter (typically in the return air duct or furnace cabinet) and inspect it. If the filter is visibly gray and compacted with debris, replace it with a new filter of the same size and MERV rating. After replacing the filter, wait 30 minutes for the furnace to cool before attempting to restart.
Condensate drain (high-efficiency furnaces only): High-efficiency furnaces (90%+ AFUE) produce condensate water as a byproduct of combustion. If the condensate drain line becomes clogged, a float switch shuts the furnace down to prevent water overflow. Check the condensate drain pan (typically a white plastic pan beneath the furnace) for standing water. A clogged drain is a job for a professional, but identifying it helps the technician arrive prepared.
Step 3: Call a Licensed HVAC Professional
If the basic checks above do not restore furnace operation, the problem requires professional diagnosis. Do not attempt to open the furnace cabinet, inspect the heat exchanger, or manipulate gas valves or ignition components yourself. Gas furnace components involve combustion, pressurized gas, and high-voltage electrical systems that present serious injury and fire risks to untrained individuals.
After Hours Heating & Cooling answers emergency calls 24 hours a day at 618-418-4118. We aim for an approximately 2-hour response time for emergency calls throughout our service area, and we do not charge extra for nighttime or weekend service — our rate is the same regardless of when you call.
When you call, have the following information ready to help your technician arrive prepared: the furnace brand and model number (typically on a label inside the furnace cabinet door), the approximate age of the system, and a description of what happened — any sounds, smells, or error codes displayed on the furnace control board.
Step 4: Keep Your Household Safe While Waiting
While waiting for your technician, take steps to maintain safe temperatures in your home:
Close interior doors to concentrate residual heat in the rooms where household members will wait. Electric space heaters can supplement warmth in occupied rooms — keep them at least three feet from flammable materials, never leave them unattended, and do not use them in rooms where children or pets are sleeping unsupervised. The U.S. Consumer Product Safety Commission (CPSC) identifies space heaters as a leading cause of home fire deaths; use them cautiously and only as a temporary measure.
Do not use gas ranges, ovens, or outdoor grills to heat your home. These appliances are not designed for space heating and produce dangerous levels of carbon monoxide in enclosed spaces. The Illinois Emergency Management Agency specifically warns against this practice.
If indoor temperatures drop below 55°F and your household includes infants, elderly individuals, or people with cardiovascular or respiratory conditions, consider relocating to a neighbor's home, a hotel, or a public warming center. The Illinois Department of Public Health notes that prolonged exposure to cold indoor temperatures poses particular risks for these populations.
What to Expect From a Professional Emergency Service Call
A licensed HVAC technician responding to a furnace emergency will typically begin with a visual inspection of the furnace cabinet, control board error codes, and flue connections. Common causes of sudden furnace failure include igniter failure (the most frequent cause in furnaces over 7 years old), flame sensor fouling, pressure switch failure, and control board faults.
Many emergency repairs can be completed in a single visit when the technician arrives with common replacement parts. After completing the repair, a professional technician should perform a combustion safety check — verifying that the heat exchanger is intact and that combustion gases are properly venting before leaving the home.
After Hours Heating & Cooling serves Belleville, Edwardsville, Troy, Godfrey, Highland, East St. Louis, O'Fallon, Swansea, and all of Metro East Illinois. Call 618-418-4118 any time — day or night, same rate.
Disclaimer: This article provides general guidance for homeowners facing HVAC emergencies and does not substitute for professional HVAC service or emergency response. For gas leaks, carbon monoxide alarms, fire, or any situation involving immediate risk to life or property, call 911 immediately. Never attempt to repair a gas furnace, gas line, or any gas appliance yourself. After Hours Heating & Cooling is licensed and insured in the state of Illinois.
This article provides general guidance for homeowners facing HVAC emergencies. It does not substitute for professional HVAC service. For gas leaks, carbon monoxide alarms, or any situation involving fire or structural risk, call 911 immediately. Never attempt to repair a gas furnace yourself.