Gas Water Heater Won't Ignite: Troubleshooting Guide

No Hot Water? Start Here

When your gas water heater refuses to ignite, you're stuck without hot water — and the list of possible causes can feel overwhelming. But in practice, most ignition failures come down to a handful of common problems, and many of them are things you can diagnose (and sometimes fix) yourself without calling a plumber.

This guide walks through the most likely causes in order of frequency, explains what to look for, and tells you when it's time to call a professional.

Before You Start: Safety First

Gas appliances require caution. Before troubleshooting:

• If you smell gas — do not attempt any repairs. Leave the house immediately, don't flip any switches, and call your gas company from outside.
• Turn the gas control knob to "off" and wait at least 5 minutes before doing any work. This allows residual gas to dissipate.
• Keep flammable materials away from the water heater area.
• Make sure the area is well-ventilated.
• If you're uncomfortable working with gas at any point, stop and call a licensed plumber. There's no shame in that.

1. Check the Gas Supply

This sounds obvious, but it's the first thing to rule out — and it's overlooked more often than you'd think.

What to Check

• Gas valve position: The shutoff valve on the gas line leading to your water heater should be fully open. The handle should run parallel to the pipe (perpendicular = off).
• Other gas appliances: Do your stove, furnace, or fireplace work? If nothing else in the house has gas, the problem may be at the meter or with your gas provider.
• Gas meter valve: Make sure the main meter valve hasn't been turned off.
• Propane tank (if applicable): Check that it isn't empty.

If you've confirmed gas is flowing to the unit, move on to the next step.

2. Try the Reset Button

This is the single most overlooked fix. Many gas water heaters have a high-limit reset button (also called a thermal switch or ECO — Energy Cut-Off) that trips when the unit overheats or detects a problem.

How to Find and Reset It

• Look for a small button behind a rubber plug on the gas control valve or near the thermostat.
• On some models, you'll need a thin probe (like a pen tip) to press it through a small hole.
• Press firmly until you feel or hear a click.
• Try relighting the pilot after resetting.

If the reset button trips repeatedly, don't just keep pressing it — there's an underlying problem (usually a faulty thermostat or gas valve) that needs to be addressed.

3. Dirty or Clogged Pilot Tube

The pilot tube is a small metal line that delivers gas to the pilot light. Over time, dust, dirt, spider webs, and debris can partially or fully block it, preventing enough gas from reaching the pilot to ignite.

How to Fix It

1. Turn the gas control knob to "off" and wait 5 minutes.
2. Remove the access panel at the bottom of the water heater to expose the burner assembly.
3. Locate the thin pilot tube — it runs from the gas control valve to the pilot light area.
4. Use a thin needle, sewing pin, or compressed air to gently clear the opening of the tube.
5. Blow through the tube gently or use canned air to clear any remaining debris.
6. Reassemble and attempt to relight the pilot.

A clean pilot tube should produce a steady, small blue flame when lit. If the flame is yellow, orange, or flickering, the tube may still be partially blocked.

4. Faulty Thermocouple

The thermocouple is a safety device that detects whether the pilot light is burning. It generates a tiny electrical signal when heated by the pilot flame, which tells the gas valve to stay open. If the thermocouple is dirty, misaligned, or worn out, it can't sense the flame — and the gas valve shuts off as a safety measure.

Symptoms

• Pilot lights but goes out as soon as you release the control knob
• Pilot won't stay lit even after holding the knob down for 60+ seconds

How to Fix It

• Clean it: Use fine sandpaper or steel wool to gently clean the tip of the thermocouple. Soot and oxidation buildup can prevent it from sensing heat properly.
• Check alignment: The thermocouple tip should sit directly in the pilot flame. If it's been bumped or shifted, it won't heat up enough. Carefully bend it back into position.
• Replace it: Thermocouples are inexpensive ($10-15 at any hardware store) and straightforward to replace. Unscrew the old one from the gas valve, remove it from the bracket, and install the new one in the same position.

5. Faulty Igniter (Piezo or Electronic)

The igniter is what creates the spark to light the pilot. There are two common types:

• Piezo igniter: A manual button you press that generates a spark mechanically. No batteries or electricity needed.
• Electronic igniter: Battery-powered or wired, creates a spark automatically when the unit calls for heat.

How to Test It

1. Darken the room and look through the viewing window at the bottom of the water heater.
2. Press the igniter button. You should see a visible spark near the pilot burner.
3. No spark = the igniter needs attention.

How to Fix It

• Clean the igniter tip: Use a soft brush to remove dust and debris.
• Check wire connections: Loose or corroded wires are a common culprit. Make sure connections are tight and clean.
• Replace the battery: If your unit has a battery-powered igniter (usually near the igniter button), replace the battery. This is one of the easiest fixes and is missed surprisingly often.
• Replace the igniter: Replacement igniters cost $15-30 and are available at hardware stores or online for your specific model.

6. Clogged Burner Assembly or Flame Arrestor

The burner assembly is where the main flame burns to heat the water. The flame arrestor is a fine mesh screen at the base of the water heater that prevents flashback but also catches dust, lint, and pet hair over time.

Symptoms

• Pilot lights fine, but main burner won't ignite
• Burner ignites briefly then goes out
• Weak or uneven flame pattern
• Soot or black marks around the burner area

How to Fix It

1. Turn off gas and let the unit cool completely.
2. Remove the access panel and burner assembly (usually held by a few screws).
3. Vacuum the flame arrestor screen at the base of the unit thoroughly.
4. Use a soft brush or compressed air to clean the burner ports (the small holes where flames come out).
5. Check for rust or damage — if the burner is cracked or heavily corroded, it needs replacement.
6. Reassemble and test.

7. Bad Gas Control Valve

The gas control valve is the "brain" of your gas water heater. It regulates gas flow, controls the thermostat, and manages safety shutoffs. When it fails internally, gas can't reach the burner properly — even if the pilot stays lit.

Symptoms

• Pilot lights but main burner never kicks on
• No clicking sound when you turn the temperature up
• Temperature control knob feels unresponsive
• Error codes on the status light (if equipped)

How to Fix It

Gas control valve replacement is not a DIY job. It requires disconnecting gas lines, and improper installation creates a serious safety risk. Call a licensed plumber. Expect to pay $150-200 for the part plus labor.

If your water heater is older than 10 years and needs a new gas valve, it's worth considering whether replacing the entire unit makes more financial sense.

8. Blocked Exhaust Vent

Gas water heaters need proper ventilation to operate. The exhaust vent carries combustion gases (including carbon monoxide) out of your home. If it's blocked, the unit may fail to ignite or shut down as a safety precaution.

Common Blockages

• Bird nests or animal debris in the vent pipe
• Disconnected or sagging vent sections
• Snow or ice buildup on the vent cap (in cold climates)
• Improper vent installation (too many bends, wrong diameter)

How to Fix It

Inspect the vent pipe from the top of the water heater to where it exits the roof. Look for obvious blockages, disconnections, or damage. Clear any debris and make sure all sections are properly connected and sloping upward.

Warning: If you suspect carbon monoxide exposure (headaches, dizziness, nausea near the water heater), leave the house immediately and call 911. Install CO detectors near all gas appliances if you don't have them.

Quick Diagnostic Checklist

Run through this list before calling a plumber — it covers the most common and easiest fixes:

1. Is the gas valve fully open? (Handle parallel to pipe = open)
2. Do other gas appliances in the house work?
3. Have you tried the reset button?
4. Does the igniter produce a visible spark?
5. Does the igniter need a new battery?
6. Is the pilot flame blue and steady (not yellow or flickering)?
7. Is the thermocouple clean and positioned in the pilot flame?
8. Is the flame arrestor screen clogged with dust or lint?
9. Is the exhaust vent clear and properly connected?

When to Call a Professional

Call a licensed plumber or HVAC technician if:

• You smell gas at any point during troubleshooting
• The gas control valve needs replacement
• The reset button keeps tripping
• You've worked through this entire checklist and the unit still won't light
• You see error codes flashing on the status indicator light
• There's water leaking from the tank (this typically means the tank has failed)
• You're not comfortable working with gas appliances

Cost Reference

Here's what common repairs typically cost so you can weigh repair vs. replacement:

• Thermocouple replacement: $10-15 (DIY) or $100-150 (professional)
• Igniter replacement: $15-30 (DIY) or $100-150 (professional)
• Gas control valve: $150-200 parts + $100-150 labor
• Professional diagnostic visit: $75-150 (often waived if you proceed with repair)

If repair costs approach 50% of a new unit's price — or your water heater is over 10 years old — replacement is usually the better investment.

How Old Is Your Water Heater?

Age matters when deciding between repair and replacement. A 5-year-old unit with a bad thermocouple is worth fixing. A 12-year-old unit with a failed gas valve? Probably time for a new one.

Not sure when yours was made? Use our free Water Heater Age Checker — just enter your brand and serial number to find out instantly.