Water Heater Pilot Won't Stay Lit

Common Symptoms

• Pilot lights when button is held down but goes out when button is released
• No hot water — water heater not firing at all
• Had to relight the pilot multiple times recently
• Pilot flame is very small or weak-looking
• Thermocouple tip is covered in carbon/soot deposits

Most Likely Causes

1. 1

   Failed Thermocouple (Most Common)

   Thermocouples have a lifespan of 3–7 years under normal use. As the internal thermoelectric junction degrades, output millivolts drop below the threshold needed to hold the gas valve open. The valve shuts off pilot gas as soon as you release the button — which is exactly how the safety system is designed to work when sensing a weak or absent pilot flame.

2. 2

   Thermocouple Tip Not in the Pilot Flame

   The thermocouple tip must be positioned directly in the pilot flame — typically 3/8 to 1/2 inch into the blue part of the flame. If the pilot burner orifice is partially clogged or the thermocouple bracket has shifted, the tip may be outside the flame and generating minimal voltage even on a new thermocouple.

3. 3

   Dirty Pilot Orifice

   A partially blocked pilot orifice produces a weak, unstable flame that doesn't consistently heat the thermocouple to operating temperature. Dirt, rust particles, or spider webs in the pilot tube are common causes. A small blue flame that flickers or has yellow tips instead of a solid cone indicates a dirty orifice.

4. 4

   Draft or Air Currents

   Strong air currents near the water heater — from nearby HVAC vents, an open door, or improper venting — can repeatedly extinguish the pilot. If the pilot goes out only in certain seasons or weather conditions, check for air movement near the base of the heater and ensure the combustion air openings aren't obstructed.

Quick DIY Checks

1. 1With the pilot lit, look closely at the thermocouple tip — it should be positioned directly in the pilot flame, glowing orange-red. If it's outside the flame or only partially in it, bend the thermocouple bracket slightly to reposition the tip deeper into the flame.
2. 2Test thermocouple output with a multimeter on the DC millivolts setting. Attach the positive lead to the thermocouple output terminal on the gas valve and the negative lead to the valve body (ground). A reading below 15mV with the pilot lit confirms the thermocouple needs replacement.
3. 3Replace the thermocouple: turn gas valve to OFF, allow the pilot assembly to cool, unscrew the thermocouple compression nut from the gas valve (counterclockwise), remove the thermocouple from the pilot bracket, and install the new universal thermocouple in reverse. The entire replacement takes 15 minutes.

Repair vs Replace

Recommended Tools & Parts

• Universal Thermocouple

  24-inch universal fit thermocouple that works with most gas water heaters, furnaces, and boilers. The most common pilot outage fix.

  $12–$20

  Buy on Amazon →

• Thermocouple/Pilot Assembly Combo Kit

  Complete pilot burner assembly with thermocouple and pilot tube combined — use when individual thermocouple replacement doesn't resolve the issue or pilot bracket is damaged.

  $25–$45

  Buy on Amazon →

• Digital Multimeter

  Essential for testing thermocouple millivolt output. Any basic multimeter with a DC millivolts setting works for this test.

  $15–$30

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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