Most Likely Causes (Ranked)
Gas pipes use threaded black iron or CSST (corrugated stainless steel tubing) connections sealed with pipe dope or Teflon tape rated for gas. Over decades, the pipe dope dries, threads corrode, and vibration from nearby equipment loosens connections. The most common leak points are at unions, tees, and connections to appliances. Even a tiny gap in a gas fitting releases enough gas to create an explosive atmosphere in an enclosed space.
Flexible gas connectors (the corrugated metal lines connecting appliances to gas pipes) have a 10-20 year lifespan. Older brass connectors (pre-1990) are recalled due to cracking. CSST flexible gas tubing can be damaged by improper installation, sharp bends, or lightning strikes (if not properly bonded). Black iron pipe corrodes externally in damp environments.
When a pilot light goes out on an older appliance (water heater, furnace, fireplace), unburned gas releases into the room until the thermocouple safety shuts it off (typically 30-60 seconds). A malfunctioning thermocouple may not shut off the gas. Gas burners that don't ignite (failed igniter on a stove) also release gas during ignition attempts.
The gas meter connections and the service line from the street to the meter are the utility company's responsibility. Meter connections corrode over time, and the regulator (which reduces pressure from the main to household levels) can develop diaphragm leaks. Ground settling can stress the service line.
Even minor earthquakes or nearby construction (vibration from heavy equipment, excavation) can loosen gas fittings, crack old pipe joints, or damage CSST tubing. The damage may not be immediately apparent — a fitting loosened by vibration may take hours or days to develop a detectable leak.
How to Fix It
Evacuate and Call for Help (Do This First)
$0 (emergency)- 1If you smell gas: DO NOT flip any light switches, use phones inside, start vehicles in attached garages, or use any potential ignition source.
- 2Leave the house immediately. Take family and pets. Leave the door open to ventilate.
- 3From outside (at least 100 feet away), call 911 or your gas utility's emergency line.
- 4Do not re-enter until the gas company clears the building.
- 5The gas company will locate the leak, shut off gas if needed, and advise on repair. This service is free.
Tighten or Replace Gas Fittings (Pro Required)
$100-400 per connection- 1Gas fitting repair should only be done by a licensed plumber or gas fitter.
- 2The technician will use a gas leak detector or soapy water to pinpoint every leak.
- 3Pipe dope (gas-rated, yellow Teflon tape) is applied to re-tightened or new fittings.
- 4A pressure test verifies the entire system holds. The gas company may need to re-light pilots.
- 5By code, all gas work requires a permit and inspection in most jurisdictions.
Replace Gas Connector
$20-60 parts / $100-200 installed- 1Old connectors (especially brass, pre-1990) should be replaced with modern stainless steel flex connectors.
- 2The connector must be the correct size and length — no adapters or extensions.
- 3Never reuse old connectors when replacing appliances.
- 4Connectors should have a gas-rated shutoff valve at the wall connection.
When to Call a Professional
Natural gas + spark = explosion. Even a light switch, phone, or doorbell can create a spark sufficient to ignite a gas-air mixture.
Carbon monoxide (CO) from incomplete gas combustion is odorless and lethal. Install CO detectors on every level of your home.
If the gas smell is very strong or you hear hissing, leave immediately. Do not investigate further.
Never attempt to repair gas lines yourself unless you are a licensed professional. Gas work requires proper tools, materials, and a pressure test.
How to Prevent It
Install natural gas detectors ($25-40) near gas appliances and in the basement/utility room.
Have gas appliances professionally serviced annually.
Replace flex connectors when replacing appliances — never reuse old ones.
Know where your gas shutoff valve is (at the meter) and keep an adjustable wrench nearby. Only shut off gas in an emergency — the gas company must re-light pilots after a shutoff.
Frequently Asked Questions
Rotten eggs or sulfur. Natural gas is odorless — utility companies add mercaptan for detection. If you smell rotten eggs indoors near gas appliances, treat it as a gas leak until proven otherwise.
The gas company will locate the leak and shut off gas for free. Repair: $100-400 per fitting. Full gas pipe replacement: $1,000-5,000 depending on the home's size and pipe material.
Yes. Symptoms include headaches, nausea, dizziness, and fatigue. If multiple household members experience these symptoms simultaneously, suspect gas or carbon monoxide. Evacuate and ventilate.
Apply soapy water (dish soap + water) to every gas connection with a spray bottle. Bubbles indicate a leak. Gas detectors ($25-40) provide continuous monitoring. Never use a flame to check for leaks.