Water Heater Pilot Light Won't Stay Lit: Fixes

When your water heater pilot light won't stay lit, you get cold showers and a heater that refuses to do its job. The good news is that the most common cause — a worn thermocouple — is a cheap part and a fix many homeowners can handle. The bad news is that anything involving gas deserves caution. This guide explains how the pilot system works, walks you through safe relighting, and covers each likely culprit in order.

How a Water Heater Pilot Light Works

The pilot light is a small, constant flame that sits ready to ignite the main burner whenever the thermostat calls for heat. Its safety partner is the thermocouple, a small sensor positioned in the pilot flame. When heated, the thermocouple generates a tiny electrical current that holds the gas valve open. If the pilot goes out, the thermocouple cools, the current stops, and the valve snaps shut — cutting gas flow so unburned gas cannot accumulate.

That safety loop is exactly why a pilot that lights but will not stay lit points to the sensor side of the system. The flame is fine; the heater simply does not believe the flame is there. Understanding this narrows your troubleshooting to the thermocouple, the pilot assembly, the gas supply, and the gas control valve, roughly in that order of likelihood.

Safety First: When Not to DIY

Gas appliances demand respect. If you smell rotten eggs or sulfur anywhere near the heater, do not try to relight anything — leave the area without touching electrical switches and call your gas utility or 911 from outside. If the area around the heater shows scorch marks, melted components, or a strong gas odor that persists after the pilot area airs out, stop and call a professional.

Also skip DIY if your heater uses electronic ignition or a hot surface igniter rather than a standing pilot — those systems have different diagnostics and higher-voltage components. And never bypass, jumper, or hold open a gas valve manually. The thermocouple safety exists to prevent gas buildup, and defeating it can fill a room with unburned gas. When in doubt, a service call at standard plumber rates is far cheaper than a gas incident.

How to Relight the Pilot Light Safely

Before replacing anything, try a proper relight — many "dead" pilots just need the correct sequence. Turn the gas control knob to OFF and wait a full five minutes for any accumulated gas to dissipate. While you wait, locate the pilot assembly behind the access panel at the bottom of the heater.

After five minutes, turn the knob to PILOT, press and hold it down, and click the igniter button (or hold a long lighter to the pilot tube) until the pilot lights. Keep holding the knob down for 30 to 60 seconds so the thermocouple heats up, then release it slowly. If the pilot stays lit, turn the knob to ON and confirm the main burner fires. If it goes out the moment you release the knob, the thermocouple is not holding the valve — which leads to the next section. Try the full sequence twice; if it fails twice, move on to diagnostics rather than repeating endlessly.

Cause 1: Bad Thermocouple

The thermocouple is the culprit in roughly 80 percent of pilot lights that will not stay lit. It is a thin copper probe that sits in the pilot flame and wears out over time — typically lasting 5 to 10 years. Symptoms are textbook: the pilot lights fine while you hold the knob down, then dies the instant you release it.

Before replacing it, check two things. First, make sure the thermocouple tip is actually engulfed by the pilot flame — if it has bent away, gently reposition it. Second, check that its connection to the gas valve is snug; a loose fitting breaks the electrical circuit. If those check out, replacement is straightforward: shut off the gas, unscrew the thermocouple from the gas valve and the pilot bracket, and install a universal replacement ($15 to $30 at any hardware store). It is a 20-minute job with a wrench. After replacement, relight following the steps above.

Cause 2: Dirty Pilot Orifice or Burner

A weak, yellow, or flickering pilot flame often means a dirty pilot orifice rather than a bad thermocouple. Dust, spider webs, and corrosion narrow the tiny gas opening, producing a flame too small or too cool to keep the thermocouple hot. You will see the difference: a healthy pilot is a sharp blue flame wrapping the thermocouple tip, while a starved pilot is lazy, yellow, and lifts off the tube.

With the gas off, remove the pilot tube and clean the orifice with compressed air or a soft brush — never ream it out with a pin or wire, which enlarges the opening and creates a dangerous oversized flame. Also vacuum dust from the burner compartment and the air intake screen at the base of the heater, since restricted combustion air produces the same weak-flame symptoms. This cleaning is good preventive maintenance anyway; add it to your annual routine from our water heater maintenance checklist.

While you have the access panel open, take a quick look at the main burner too. A healthy gas burner shows steady blue flames with perhaps small yellow tips; large lazy yellow flames or soot marks on the burner or flue indicate incomplete combustion, which wastes fuel and can produce carbon monoxide. Soot is always a call-a-technician signal rather than a cleaning task, and it is another good reason to keep that CO detector's batteries fresh.

Cause 3: Gas Supply and Draft Problems

Sometimes the pilot is fine and the fuel delivery is not. Check that the gas shutoff valve on the supply line to the heater is fully open — a partially closed valve starves the pilot. If other gas appliances in the house are also acting up, the problem may be supply-side, and your gas utility should investigate.

Drafts are the sneakier cause. A strong downdraft down the flue — common during windstorms or when a nearby exhaust fan runs — can literally blow the pilot out or pull the flame off the thermocouple. Signs include a pilot that dies on windy days or when the dryer or range hood runs. A draft hood that is misaligned or a flue with poor draw needs a technician's eyes, since venting problems also risk carbon monoxide spilling into the home. Make sure a working CO detector is installed near any gas water heater, no exceptions.

Cause 4: Failing Gas Control Valve

If the thermocouple is new, the pilot is clean and strong, and the gas supply is good, the gas control valve itself may be failing. The valve contains an electromagnet that the thermocouple's current holds open; when that magnet weakens, no thermocouple can keep it engaged. This is less common but happens, especially on heaters past 10 years old.

Gas valve replacement is not a typical DIY job — it involves breaking gas connections and the repair runs $300 to $600 installed. At that price on an older heater, do the replacement math first: a new valve on a 12-year-old tank buys you limited time. Our water heater replacement cost guide helps you compare against a full new unit. For a broader look at heater care, see our water heater guides.

When to Call a Professional

Call a licensed plumber or HVAC technician if you smell gas, if the pilot will not stay lit after a thermocouple replacement and cleaning, if the gas valve is suspect, or if the heater is over 12 years old and developing multiple problems at once. Also call if you are simply uncomfortable working around gas — there is no shame in that, and it is the right call.

A diagnostic visit typically runs $75 to $150, with thermocouple replacement during the visit adding $100 to $200 in labor. If the heater needs a gas valve or is simply at end of life, get the full picture before authorizing a big repair. For after-hours emergencies like a suspected gas leak or a failed heater flooding the area, our emergency plumber cost guide covers what to expect.