Short definition

Lighting the pilot on a standing-pilot gas water heater is a sequence printed on the appliance itself: gas valve to PILOT, depress and hold the pilot button, ignite with the piezo or a long match, hold 30–60 seconds for the thermocouple to warm, release, then turn the valve to ON. The single most important rule: do not attempt ignition if you can smell gas.

What it is

A standing-pilot gas water heater keeps a small flame burning continuously next to a thermocouple — a sensor that produces a tiny electrical signal when heated. That signal holds open a safety valve in the gas-control body. When the burner needs to fire, gas flows past the still-lit pilot, ignites, and heats the tank.

If the pilot goes out — wind through the draft hood, dust on the orifice, an aging thermocouple — the safety valve closes. No pilot, no burner, no hot water. Relighting is the homeowner reset.

The procedure is manufacturer-specific and printed on a placard on the front of the heater. Bradford White, Rheem, A.O. Smith, and the rest all use the same general sequence with small variations. Read the placard.

Modern units (post-2003 FVIR-listed) have a sealed combustion chamber with a flame arrestor screen and a piezo igniter — no match required. Older units may need a long match through a viewport. Tankless and electronic-ignition tank heaters do not have a homeowner pilot procedure; they re-ignite automatically and show error codes when they can’t.

Why it matters to a homeowner

A pilot relight is a 5-minute homeowner job in the 90% case. A pilot that won’t stay lit after relight is usually a thermocouple — a $15 part, $80–$150 service call. There’s no reason to wait two days for a plumber if you understand the rule and the procedure.

The rule is short: never attempt ignition if you can smell gas. Wait for the smell to clear. If it doesn’t clear in a few minutes with the gas valve in OFF, leave the house and call the utility. Lighting a flame in a room with detectable gas is the worst-outcome version of this task.

When you’ll encounter this term

  • Brand-new water heater install — first ignition takes longer than a relight because the gas line still has air in it
  • Returning from vacation where gas was shut off
  • Pilot blown out during a windstorm — relight, but if it blows again within hours, address combustion-air drafting
  • Recurring pilot outage after relight — the thermocouple is the most likely culprit

The procedure (general — read your placard)

  1. Smell first. Kneel down and smell near the floor for 60 seconds. Gas is heavier than air on propane systems, lighter than air on natural gas — but mercaptan accumulates near the appliance regardless. If you smell anything, stop. Do not proceed.
  2. Turn the gas valve to OFF, wait at least 5 minutes for any residual gas to clear.
  3. Turn the gas valve to PILOT.
  4. Depress and hold the pilot button. This manually feeds gas to the pilot orifice only.
  5. Press the piezo igniter (or insert a long match through the viewport).
  6. Once the pilot lights, keep holding the pilot button for 30–60 seconds. The thermocouple needs to warm and energize the safety valve.
  7. Release the button. If the pilot stays lit, turn the gas valve to ON. Burner will fire when the thermostat calls for heat.
  8. If the pilot goes out when you release, repeat. On a brand-new install, repeat several times — air bleeds through the orifice over multiple attempts.

Common reasons a pilot won’t stay lit

  • Thermocouple failure. Most common. $15 part, $80–$150 to replace.
  • Flame-arrestor screen blocked by dust or lint on FVIR units. Vacuum the screen; if persistent, full clean-out service.
  • Gas valve magnet failed. Replace the gas valve assembly.
  • Gas pressure too low. Utility issue or partially closed shutoff upstream.
  • Drafty utility room blowing the pilot out. Address combustion-air supply.
  • Air still in line on a new install. Keep relighting; air bleeds out.

When to stop and call

  • If the pilot won’t ignite after 2–3 attempts and there’s no smell of gas, the thermocouple is likely failed. Service call.
  • If you smell gas at any point, stop. Wait for the smell to clear with the valve OFF, or leave and call the utility.
  • If the unit has been involved in a flood or earthquake, gas-line integrity is unknown — do not relight. A pro pressure-tests the system first.
  • If the unit is electronic-ignition (no continuous pilot, just a “click-click” at startup) and won’t fire, there is no homeowner relight procedure. Check the error code, then service call.

Common variants

  • Standing pilot — the procedure above. Continuous flame; thermocouple-monitored.
  • Electronic ignition — newer water heaters. No standing pilot. The unit sparks on demand. No homeowner pilot procedure; troubleshoot via error code.
  • Hot-surface ignition — rare in residential water heaters; common in furnaces.
  • Tankless — almost universally electronic ignition. Lighting the pilot doesn’t apply.