When your water heater stops working after installation or repairs, trapped air in the gas line is often the reason. Air pockets prevent the gas from flowing smoothly, so the pilot won’t light or the burner won’t stay on. Many homeowners face this problem, but not everyone knows how to safely purge air from the gas line.
Learning how to do this can save you time, money, and avoid calling a professional for a simple fix.
This guide gives you clear, step-by-step instructions to purge air from the gas line on your water heater. You’ll understand the tools you need, safety tips, the detailed process, and common mistakes to avoid. Even if you’re not a plumber, you’ll see that with careful steps, this task is manageable.
Along the way, you’ll get practical advice that even experienced DIYers sometimes overlook.
Why Air Gets Trapped In Gas Lines
Air can enter your water heater’s gas line during repairs, installation, or if the gas supply was shut off. When a new water heater is installed, the gas line will be empty and full of air. If gas utility work happens nearby, you might also have air in your line when service resumes.
Trapped air blocks the flow of natural gas or propane to the burner. This means your water heater can’t heat water, and you may hear hissing or clicking with no ignition. Purging is the process of removing this air so that gas can flow smoothly again.
Is It Safe To Purge Air Yourself?
If you follow the right steps, purging air from a gas line is generally safe for most homeowners. However, gas is flammable and mistakes can be dangerous. If you smell a strong odor of gas, hear hissing, or feel unsure, stop and call a professional immediately.
For basic air purging, you usually don’t need special licenses, but always check your local regulations. Some regions require a certified technician. When working with propane, extra care is needed because propane is heavier than air and can collect in low spots.
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Tools And Materials You’ll Need
Before you start, gather all tools and safety items. Having everything ready makes the process smoother and safer.
- Adjustable wrench – For loosening and tightening gas connections.
- Soapy water solution – Mix dish soap with water in a spray bottle to check for leaks.
- Flashlight – To see behind and around your water heater.
- Towel or rag – In case of small spills.
- Long lighter or igniter – For pilot lighting (if manual).
- Gas leak detector (optional) – For extra safety.
- Work gloves – To protect your hands.
- Screwdriver – For opening access panels.
Never use open flames to check for leaks, and avoid using electrical switches if you smell gas.
Essential Safety Steps
Working with gas lines demands strict attention to safety. Here’s what you need to do before starting:
- Shut off the gas supply at the main valve if you smell gas.
- Ventilate the area by opening windows and doors.
- Do not smoke or use lighters near the water heater.
- Keep children and pets away from the work area.
- Have a fire extinguisher nearby, just in case.
If you ever feel unsure, stop and call your utility company or a licensed plumber.
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Understanding Your Water Heater’s Gas System
It helps to know how your water heater’s gas system works. Most residential water heaters use either natural gas or propane.
- The gas enters from the main supply line.
- It passes through a shutoff valve near the heater.
- Gas moves into the control valve and then to the pilot light or burner.
Many modern heaters have electronic ignition, while older models use a standing pilot light. You’ll need to know which type you have before starting.
Comparison: Natural Gas Vs. Propane Water Heaters
Here’s a quick look at the differences that matter when purging air:
| Feature | Natural Gas | Propane |
|---|---|---|
| Gas Density | Lighter than air | Heavier than air |
| Odor | Distinct, added odorant | Distinct, added odorant |
| Purging Process | Air rises, easier to vent | Air falls, harder to vent |
Knowing which type you have helps you understand how air and gas move during purging.
Step-by-step Guide: How To Purge Air From Gas Line On Water Heater
Purging air from the gas line is a process. Follow these steps carefully for safety and effectiveness.
1. Turn Off The Gas Supply
Locate the gas shutoff valve near your water heater. Turn the valve to the “off” position so no gas flows while you work. If you’re not sure where this is, trace the pipe from the heater back to the wall.
2. Wait And Ventilate
Open windows and doors to let any gas in the area escape. Wait at least five minutes before starting to ensure the space is safe. This step is easy to overlook but essential for safety.
3. Access The Pilot Or Burner Area
Remove the access panel at the base of the water heater using your screwdriver. This gives you a clear view of the pilot assembly or burner area.
4. Loosen The Pilot Tube Fitting (if Accessible)
Some heaters have a small fitting or nut on the pilot tube. Using an adjustable wrench, gently loosen this fitting. This lets trapped air escape from the line.
- For newer heaters, this step may not be needed, as the control valve often vents air as you light the pilot.
5. Turn The Control Valve To Pilot
Set the control knob to the “pilot” position. Hold it down to start the flow of gas. On electronic models, press and hold the ignition button.
6. Purge The Air
While holding the pilot knob, try to ignite the pilot using your long lighter or igniter. It may take several tries before the pilot lights. Each time you hold the knob, a small amount of gas pushes air out of the line.
- If the pilot doesn’t light after 60 seconds, stop and wait a few minutes, then try again.
- For heaters with a manual pilot tube fitting, you may hear a faint hiss as air escapes. When you start to smell gas, tighten the fitting.
7. Light The Pilot
When the pilot flame finally lights, keep holding the control knob for 30-60 seconds. This heats up the thermocouple, which tells the system gas is burning safely.
8. Check For Leaks
Spray the soapy water solution on all fittings you loosened. If bubbles form, there’s a leak—tighten the fitting and test again. Do not skip this step.
9. Restore Normal Operation
Turn the control knob to the “on” position. Replace the access panel. Turn the main gas valve back to “on” and listen as the burner ignites.
10. Monitor The Water Heater
Watch your water heater for the next 10-15 minutes. Make sure the burner stays lit and there are no strange noises or smells. If you notice problems, shut everything off and call a professional.
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Common Mistakes And How To Avoid Them
Purging air from a gas line seems simple, but there are some frequent errors even experienced DIYers make:
- Skipping leak tests – Never assume a connection is tight. Always check with soapy water.
- Rushing the process – Lighting the pilot too soon can cause a small “pop” or fail to ignite at all.
- Forgetting to ventilate – Trapped gas is dangerous. Always air out the room first.
- Over-tightening fittings – This can damage threads and cause leaks later.
- Not relighting the pilot – Some homeowners forget the last step, and the heater stays off.
Taking your time and following each step reduces these risks.
How Long Should Purging Take?
In most cases, purging air from a gas line should take about 10–20 minutes. Heavily air-filled lines or long gas pipes may take longer. If you’ve tried several times and the pilot still won’t light, stop and seek help. Don’t keep releasing gas indefinitely.
When To Call A Professional
While many homeowners can purge air themselves, call a licensed plumber or gas technician if:
- The pilot still won’t light after several attempts.
- You smell a persistent gas odor.
- You hear hissing from pipes or fittings.
- You feel dizzy or lightheaded while working.
- Local regulations require a licensed pro.
Remember, safety always comes first. It’s better to spend a little more than risk a dangerous mistake.
Special Considerations For Propane Water Heaters
Propane behaves differently than natural gas. Because propane is heavier than air, it can collect near the floor or in basements. If you have a propane system:
- Always purge air outdoors if possible.
- Check for propane-specific safety devices and valves.
- Use a propane leak detector if available.
If you ever suspect a propane leak, leave the area and call your supplier immediately.
Troubleshooting: If The Pilot Still Won’t Light
Sometimes, the pilot won’t light even after purging air. Here’s what to check next:
- Thermocouple – This safety device can fail, preventing the pilot from staying lit.
- Clogged pilot orifice – Dirt or debris can block gas flow.
- Gas supply valve – Make sure it’s fully open.
- Incorrect gas type – Heaters set for natural gas won’t work with propane and vice versa.
- Faulty control valve – If the control valve is broken, it won’t allow gas through.
If you’ve checked all of these and still have no luck, it’s time to call a pro.
How Often Should You Purge Air?
You only need to purge air from the gas line when:
- Installing a new water heater
- Replacing gas lines or fittings
- After a gas supply interruption
It’s not a routine maintenance task, so don’t do it unless you have a reason.
Real-world Example: What A Diy Homeowner Learned
After installing a new water heater, John noticed the pilot wouldn’t light. He followed the steps for purging air but rushed through the leak check. A week later, he smelled gas and discovered a slow leak at a fitting. After tightening and retesting, the problem stopped. John realized that testing for leaks is just as important as purging air.
This kind of oversight is common. Taking time for each step, especially safety checks, prevents bigger problems later.
What If You Have A Tankless Water Heater?
Most tankless water heaters also use gas lines, but their ignition systems are usually electronic. Air in these lines can cause ignition errors or fault codes.
- Follow the same purging steps: Shut off gas, ventilate, open access panels, and purge air by attempting ignition.
- If the unit displays an error code, check the manual for troubleshooting.
- Always test for leaks after working on the gas line.
Tankless models may take longer to purge if the lines are long.
Tips For Success (that Most Beginners Miss)
- Purge during daylight – Good lighting helps you spot leaks and see pilot flames.
- Label gas valves – Mark the “on” and “off” positions with tape if it’s not obvious.
- Keep the manual handy – Each water heater is a bit different; your owner’s manual has model-specific info.
- Record the process – Taking notes or photos helps if you need professional help later.
These small habits make troubleshooting and future repairs much easier.
Understanding Gas Line Sizes And Purging Time
The size and length of your gas line affect how much air must be removed. Here’s a look at approximate times for different line lengths:
| Gas Line Length | Purge Time (average) | Notes |
|---|---|---|
| Up to 10 feet | 5–10 minutes | Quickest purge |
| 10–30 feet | 10–20 minutes | Standard home setup |
| Over 30 feet | 20–30 minutes | May require extra attempts |
Longer lines mean more air to remove, so be patient and don’t rush.
Gas Leak Detection: Soapy Water Vs. Electronic Detectors
Which method is better for checking leaks after purging? Here’s a comparison:
| Detection Method | Pros | Cons |
|---|---|---|
| Soapy water | Cheap, easy, effective | Can miss tiny leaks, messy |
| Electronic detector | Very sensitive, quick | Costly, needs batteries |
For most homeowners, soapy water is enough. For peace of mind, consider an electronic detector—especially if you have kids or elderly family members at home.
Final Checklist Before Finishing
Before you call the job done, make sure you:
- Double-check all fittings for leaks.
- Confirm the pilot and burner stay lit.
- Replace all access panels and tools.
- Leave the area clean and clear of debris.
- Review your water heater’s manual for any special instructions.
If everything checks out, your water heater is ready to deliver hot water again.
Where To Learn More
If you want to understand more about gas safety, maintenance, and water heaters, check resources like the U.S. Department of Energy. They provide trusted, up-to-date advice for homeowners.
Frequently Asked Questions
How Do I Know If Air Is Trapped In My Water Heater’s Gas Line?
Common signs are your pilot won’t light, you hear clicking but no ignition, or you smell gas after several attempts. If your heater worked before but stopped after repairs or installation, air is likely trapped.
Is It Dangerous To Try To Purge Air Myself?
It can be, if you don’t follow safety steps. Always ventilate, test for leaks, and stop if you smell strong gas. If you’re ever unsure, call a professional.
How Long Should I Try To Purge Air Before Stopping?
Usually, purging should not take longer than 20 minutes. If you’ve tried several times and the pilot won’t light, stop and seek help. Don’t keep releasing gas without results.
What Should I Do If I Smell Gas After Purging?
Turn off the gas supply, open windows, and leave the area. Do not use electrical switches or flames. Call your gas company or a licensed plumber immediately.
Can I Use My Water Heater Right After Purging Air?
Yes, if you’ve confirmed there are no leaks, the pilot and burner stay lit, and everything is back in place. Monitor the heater for the next 15 minutes to ensure safe operation.
Getting air out of your water heater’s gas line is a practical skill. With the right tools, careful steps, and respect for safety, most homeowners can handle this job themselves. Take your time, double-check your work, and you’ll have hot water flowing again soon.