Wet Gas Water Heater Pilot Won't Light
The Short Answer: A gas tank that got wet will not light because the pilot, thermocouple, and FVIR screen are drowned — or because tank water is in the combustion chamber and the vessel is scrap. Shut the gas cock. Do not keep clicking the piezo. Rain after a storm is a different page. Flood, a hose, or the tank leaking into its own burner is this one.
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Search Intent & The Real Problem
The basement took on water. A supply line blew. Someone washed the garage and soaked the jacket. Or the tank has been weeping into the burner tray and you only noticed when the pilot died. People search this and get “hold the knob longer” and a $12 thermocouple. A wet millivolt circuit does not latch. A wet FVIR arrestor does not pass air. Water in the combustion chamber is a carbon monoxide problem if you keep firing it.
Weather-only deaths: gas after rain. Crawl installs that sit in a puddle every spring: crawl-space failures. Cold snap, no flood: pilot in cold weather. Electronic ignition that never clicks: Honeywell no spark, piezo.
What other guides get wrong
They tell you to towel the thermocouple and relight while the arrestor is still a sponge. They sell a thermocouple for a tank that has a rust ring at the burner — that is a hole in the tank, not a millivolt part. They garden-hose the flue “to rinse mud,” which floods the chamber again. They treat a flooded power-vent the same as a standing-pilot millivolt valve. And they skip the source: if the tank itself is the puddle, lighting it is how you make CO and a second flood.
Step-by-Step Troubleshooting
Step 1: Shut energy. Name the water. Decide if you even relight
| What you see | Meaning | Relight? |
|---|---|---|
| Standing water at the base, jacket wet, rust at the seam | Tank or a fitting above — bottom leak | No |
| Water / mud in the burner tray, rust ring at the chamber | Tank leaking into combustion, or flood that sat | No. Gas off. |
| FVIR screen under the burner soaked, tray otherwise dry | External water (flood, hose, rain cap) | Not until dry |
| Pilot assembly dripping, thermocouple wet, screen dry | Condensate, T&P, or a fitting tracking down | Find the drip first |
| Power-vent blower housing wet, switch hissing | Water in the fan / pressure tube | Do not fire it |
| Only after a storm, outdoor / crawl | Weather path | After rain |
- What to look for: Gas cock off. Control to off. If the closet flooded near electric, stay out until it is dry. Photo of the burner door before you mop — rust ring vs clean wet metal is the whole diagnosis.
- Required tools: Flashlight, paper towel. No match. No piezo marathon.
Step 2: Kill the incoming water that is still feeding it
- What to look for: Cold inlet still open on a tank that is weeping into the burner. A connector or SharkBite on the head tracking into the draft hood and down the flue. T&P discharge that has no pipe, dumping onto the jacket — never cap that valve; route it, or shut the tank down. House static over ~80 psi with a waterlogged expansion tank will keep a T&P dribbling. Typical relief 150 psi / 210°F.
- Required tools: Inlet valve. Hose-bib gauge if the T&P is the source. Pan.
You do not empty a 50-gallon to diagnose a drowned pilot. You stop the flood.
Step 3: Standing-pilot path — wet millivolts
- What to look for: Piezo click with no spark: wet electrode, not a new valve. Spark, no flame: orifice full of water or a cock that is off. Flame that will not kiss the thermocouple: tip under water or bent. Flame that lights and dies when you release: wet thermocouple that cannot make ~20–30 mV, or a flooded FVIR so the flame is yellow and lazy. Thermopile valves need hundreds of mV — confirm the valve, do not guess. Brand pilots: Whirlpool, GE, generic won’t stay lit.
- Required tools: Eyes through the viewport. Jacket lighting sticker. A licensed tech’s meter for millivolts. You do not hold the knob for ten minutes “to dry it.”
A packed wet arrestor looks like a bad thermocouple. It is air. Relighting into a wet screen is delayed ignition and a bang — loud bang.
Step 4: Electronic ignition and power-vent — water plus 120 V
- What to look for: Honeywell / White-Rodgers hot-surface or spark that sits silent after a flood: water in the control, a drowned flame rod, or a pressure switch open because the vinyl tube is full. LED flash charts after a soak are often chamber / FVIR — chamber sensor, Honeywell reset. Power-vent: blower must spin before the valve opens. A wet fan is CO if you jumper the switch. After a storm outage on the same night: gas after power outage.
- Required tools: Eyes on the blower wheel (cover on). Photo of any LED. No jumper.
Manifold pressure is licensed (about 3.5–7 in. w.c. natural gas / 10–11 in. w.c. LP — confirm the rating plate). Do not crack unions to “blow it out.”
Step 5: Dry vs scrap — when the tank is finished
- What to look for: External flood, tray wiped, arrestor dry, no rust ring, millivolt circuit intact: a licensed tech can relight after the chamber is actually dry, not after one afternoon with a shop fan. Rust ring, scale stalactites in the burner, water returning with every fitting above dry: the glass lining failed into the flue or the bottom head. That tank is replacement. Same-day licensed swap beats a CO event. Water tracking from the vent collar is a different drip — vent collar.
- Required tools: None for the scrap call. Do not epoxy the combustion chamber.
When DIY Ends: Calling a Licensed Pro
You may close the gas cock, close the cold inlet, photograph the burner tray, and get out of a flooded closet. Stop at gas odor, water in the chamber, a rust ring, a silent power-vent, and any “dry it with the burner on.” Thermocouple, FVIR, gas-valve, and vent work after a flood are licensed. A drowned $12 thermocouple on a sound tank is a service call. A tank that filled its own burner is a permitted replacement.
Frequently Asked Questions
Q: Why won’t my gas water heater pilot light after it got wet? A: The thermocouple and FVIR screen are drowned, the piezo is wet, or tank water is in the combustion chamber. Shut the gas. Do not keep clicking it. A rust ring at the burner means the tank is done.
Q: Can I light a gas water heater that got wet? A: Not while the chamber is wet, and never if water is in the burner tray. External spray that has fully dried, with a clean arrestor and no rust ring, is a licensed relight. Flooded controls are replacement.
Q: Is a wet pilot the same as a water heater that died after rain? A: Same physics, different source. Rain down a B-vent or a missing cap is the weather article. This page is flood, a hose, or the tank leaking onto its own burner.