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Water Heater Suddenly No Hot Water? Start With the Pilot and Thermocouple

When your water heater goes from hot showers to ice cold overnight, the pilot light or thermocouple is the culprit 80% of the time. Fix it without calling a plumber.

Category:Plumbing

Difficulty:Moderate

Time:20-30 min

Success:50%

Updated:May 22, 2026

quick_referenceQuick Answer

For Water Heater Suddenly No Hot Water? Start With the Pilot and Thermocouple, start with "Check the pilot light window — is the flame there or out?": Stop cranking the gas valve back and forth — you could damage the regulator. Remove the access panel at the bottom of the tank. Look through the sight glass at the pilot assembly. If you see a small blue flame, the pilot is lit but the thermocouple may be failing. If there's no flame at all, the pilot went out and the thermocouple did its job by shutting the gas. Try relighting it once per the instructions on the tank label. If it goes out again within a minute, the thermocouple needs replacement — do not keep trying. Stop DIY if you smell gas anywhere near the water heater — turn off the gas at the meter shutoff and evacuate immediately. This is listed as a moderate recovery and usually takes about 20-30 min.

verifiedGuide Snapshot

Repair areaPlumbing

Estimated time20-30 min

DifficultyModerate

Stop conditions4

Last updated May 22, 2026. Review the stop conditions before continuing.

account_treeRecovery State

DeviceWater Heater

Current stateNo Hot Water

Specific statePilot Wont Stay Lit

Failed stepPilot Ignition

Likely failure typeSensor Fault

DIY boundaryDIY recovery first

paymentsCost decision

help1. Understand the Problem

Gas water heaters rely on a standing pilot flame to ignite the main burner. When the thermocouple — a small heat sensor next to the pilot — fails or gets coated with carbon, it can't detect the pilot flame and shuts off the gas valve as a safety measure. This often happens after the tank has been off for a while or when the unit is 5+ years old.

build_circle2. Try This First

Best First Step

Check the pilot light window — is the flame there or out?

Stop cranking the gas valve back and forth — you could damage the regulator. Remove the access panel at the bottom of the tank. Look through the sight glass at the pilot assembly. If you see a small blue flame, the pilot is lit but the thermocouple may be failing. If there's no flame at all, the pilot went out and the thermocouple did its job by shutting the gas. Try relighting it once per the instructions on the tank label. If it goes out again within a minute, the thermocouple needs replacement — do not keep trying.

visibility3. Visual Guidance

See what's happening and how to try the first recovery step.

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Turn off the gas and remove the burner assemblyTurn the gas control knob to OFF. Wait 5 minutes for any gas to dissipate. Disconnect the three lines from the gas control valve: the pilot tube, the main burner supply tube, and the thermocouple connection (finger-tight plus a quarter turn with a wrench). Slide the entire burner assembly out through the access opening.

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Replace the thermocouple and clean the pilot orificeUnscrew the old thermocouple from the bracket — one small nut holds it. Install a universal thermocouple (about $10 at any hardware store). Route it exactly as the old one was — don't kink the copper tube. Clean the pilot orifice with a wire brush and compressed air. A clogged orifice starves the pilot and kills the thermocouple even faster.

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Reassemble, leak-test, and relight the pilotSlide the burner back in, reconnect all three lines, and tighten. Mix dish soap and water in a spray bottle and spray every gas connection you touched. Turn the gas knob to PILOT, hold it down, and click the igniter. Hold for 30 seconds after the flame lights, then release. If bubbles appear anywhere, tighten that fitting immediately. Once the pilot stays lit, turn the knob to ON and set the temperature to 120°F.

autorenew4. If That Doesn't Work

Try the next recovery options.

water_drop

Flush the tank if the water is hot but runs out fastSediment buildup at the bottom of the tank displaces water volume. If you get 3 minutes of hot water then cold, the tank is full of mineral sediment. Connect a garden hose to the drain valve, run it outside or to a floor drain, and flush until the water runs clear.

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settings

Replace the gas control valve if the pilot lights but the burner never kicks onIf the pilot stays lit but the main burner never fires, the gas control valve's thermostat has failed. This is a $100-150 part and requires disconnecting and reconnecting the gas supply line. If you're not comfortable with gas piping, this is the point to call a pro.

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bolt

Check the circuit breaker on an electric water heaterElectric water heaters use two 240V elements controlled by thermostats. If you have an electric unit and no hot water, first check the double-pole breaker hasn't tripped. Then test continuity across each heating element with a multimeter — a burned-out element reads as an open circuit.

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Frequently Asked Questions

Why does my pilot light keep going out after I relight it?expand_more

A pilot that goes out repeatedly is almost always a bad thermocouple. The thermocouple generates a tiny electric current from the pilot flame's heat. When it weakens, the gas valve thinks the pilot is out and shuts everything down. A new thermocouple costs about $10 and takes 20 minutes to swap.

How do I know if it's the thermocouple or the gas valve?expand_more

Light the pilot and hold the gas knob in PILOT position for a full 60 seconds. Release. If the pilot stays lit but goes out when you turn the knob to ON, it's the gas valve. If the pilot goes out within seconds of releasing the knob even in PILOT position, it's the thermocouple.

Can I clean a thermocouple instead of replacing it?expand_more

You can gently sand the tip with fine-grit sandpaper to remove carbon buildup. This works maybe 30% of the time. But thermocouples are cheap and failing ones tend to fail again soon. If you're going through the trouble of pulling the burner assembly, just put in a new one.

What temperature should I set my water heater to?expand_more

120°F is the sweet spot. Hot enough to kill bacteria (anything below 120°F can grow Legionella), cool enough to prevent scalding (140°F+ causes third-degree burns in 5 seconds). If your dishwasher doesn't have a built-in preheat cycle, you may want 130°F, but install anti-scald valves on shower and bath faucets if you have kids.

warning5. Stop DIY If

Don't continue if any of these apply.

reportYou smell gas anywhere near the water heater — turn off the gas at the meter shutoff and evacuate immediately.

reportThe tank is leaking water from the bottom — this means the tank itself has rusted through and must be replaced by a professional.

reportThe gas control valve is hissing, the burner flame is yellow instead of blue, or you see soot around the burner area — these indicate incomplete combustion and carbon monoxide risk.

reportWater from the hot tap is rusty brown or has a rotten egg smell — the anode rod has failed and the tank may be corroding internally.

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