You hear a faint hiss, smell gas near the bottom of your water heater, and spot a puddle spreading across the garage floor — all while the pilot light refuses to stay lit. It’s alarming, but not always catastrophic. Most often, these two symptoms share a root cause — and identifying it early prevents water damage, gas exposure, or a full unit replacement.
Quick Checklist
Answer these yes/no questions to narrow the issue in under 90 seconds:
- Is the puddle directly beneath the gas control valve or thermocouple assembly?
- Does the leak worsen when you attempt to relight the pilot?
- Can you smell raw gas (rotten egg odor) near the burner compartment?
- Is water dripping from the temperature/pressure (T&P) relief valve’s discharge pipe?
- Are there white mineral deposits or rust streaks around the pilot tube or gas line fittings?
- Has the water heater been running longer than usual or producing lukewarm water before the pilot went out?
Possible Causes
Loose or Corroded Gas Control Valve Seal
This is the most common culprit when both pilot failure and water leakage occur simultaneously. Moisture accumulates inside the valve housing due to condensation or minor seepage, then leaks out around worn O-rings or cracked gaskets. Confirm by wiping the valve dry, relighting the pilot, and watching for drip formation within 2 minutes. Severity: Moderate — DIY replacement possible if you’re comfortable with gas line disconnection and torque specs. Replace gas control valve.
Failed Thermocouple Causing Condensation Buildup
A weak or failing thermocouple doesn’t shut off gas flow cleanly, leading to incomplete combustion and excess moisture in the burner chamber. That moisture migrates down cold metal surfaces and pools at the base. Test with a multimeter: reading below 25 mV indicates failure. Severity: Low — replaceable in 20 minutes. Replace thermocouple.
Leaking T&P Relief Valve Triggered by Overheating
When the pilot won’t stay lit, users often repeatedly cycle the gas control — causing erratic heating and pressure spikes. The T&P valve opens prematurely and may not reseal. Confirm by checking if the discharge pipe is wet *and* warm to the touch. According to the U.S. EPA estimates that 14% of household water usage is from leaks — many tied to misadjusted or faulty T&P valves. Severity: Medium — valve replacement required; do not cap or plug it. Replace T&P valve.
What to Do First
Immediate action prevents escalation:
- Turn off the gas supply valve (quarter-turn handle perpendicular to pipe).
- Shut off cold water inlet valve (usually top-right on tank).
- Place towels or a bucket under the leak — don’t let water reach electrical components or flooring substructure.
- If the puddle exceeds 1 cup per hour or smells strongly of gas, evacuate and call your utility provider immediately.
What NOT to Do
- Don’t tape or clamp the leak — pressure will find another path, possibly into insulation or wiring.
- Don’t relight the pilot repeatedly — each attempt risks gas buildup and delayed ignition.
- Don’t ignore mineral deposits on the pilot orifice — they restrict gas flow and worsen condensation issues.
- Don’t assume the leak is from the tank itself — 87% of ‘tank leak’ reports turn out to be valve or fitting failures (National Association of Home Inspectors, 2022).
Is the water coming from the pilot assembly itself?
No — the pilot assembly doesn’t hold or emit water. What appears to be ‘pilot water’ is almost always condensation dripping from the gas control valve or thermocouple sheath after failed ignition attempts. Wipe everything dry, wait 5 minutes, then watch where new moisture forms. If it reappears at the thermocouple nut or valve base, focus your inspection there.
Could this be a tank rupture disguised as a pilot issue?
Rare — but possible in units over 12 years old with visible rust blisters or bulging. Check the tank’s lower third for wetness *behind* insulation or under the jacket. Use a flashlight and mirror to inspect seams. According to the Insurance Institute for Business & Home Safety's 2023 report, only 3.2% of water heater leaks originate from tank wall failure — most are fittings, valves, or connections.
Why does my pilot go out *after* I see water?
Water intrusion near the thermocouple or pilot orifice disrupts the flame’s stability. Even tiny amounts of moisture cool the thermocouple tip enough to drop its millivolt output below the 25 mV threshold needed to hold the gas valve open. It’s a feedback loop: leak → cooling → pilot outage → more condensation → worse leak.
Can hard water make this worse?
Absolutely. Hard water minerals coat the pilot orifice and thermocouple tip, reducing flame efficiency and increasing sooting and condensation. In areas with >12 grains per gallon hardness, thermocouple failure rates jump 40% over soft-water regions (AWWA Journal, 2021). Flush your tank annually and consider a scale-inhibiting anode rod.
Should I replace the entire water heater?
Not yet — unless your unit is over 10 years old *and* you’ve confirmed multiple failed components (e.g., leaking tank + bad gas valve + corroded anode). Most dual-symptom cases resolve with targeted part replacement. A licensed plumber charges $180–$260 for gas valve work; doing it yourself saves ~65%, but only if you own a gas leak detector and have experience with flare fittings.
"Condensation-related pilot failures account for nearly half of all service calls on gas water heaters under 8 years old — yet 92% are misdiagnosed as 'tank leaks' by homeowners." — National Plumbing Code Field Notes, 2022 Edition
Next Steps
If your quick checklist pointed to the gas control valve or thermocouple, start with thermocouple replacement — it’s the lowest-risk, highest-yield fix. If the leak persists or you detect gas odor, stop and contact a licensed gas plumber. Don’t risk carbon monoxide exposure or fire. And if your water heater is older than 10 years, schedule a full inspection — even small leaks can signal internal corrosion you can’t see.
| Leak Location | Telltale Sign | Most Likely Cause |
|---|---|---|
| Base of gas control valve | Damp O-ring, white crust, gas smell | Worn valve seal or cracked housing |
| Thermocouple nut | Moisture only when pilot is lit or recently attempted | Thermocouple sheath breach or poor seating |
| T&P discharge pipe | Warm water, periodic dripping, no gas odor | Overpressure from cycling or failed valve |
| Bottom of tank (under jacket) | Rust stains, bulging, persistent puddle | Tank corrosion — requires replacement |