If a hot water tap drips or the heater doesn't ignite, the culprit is often a bad thermocouple. This small, metal device sits on the pilot flame of a gas water heater and keeps the gas valve open only when the pilot is lit. If it fails, your heater can shut off or even pose a safety hazard. Being aware of the warning signs can help you catch problems before they turn into costly repairs.

1. Pilot Light Frequently Extinguishes
The most obvious sign is that the pilot flame repeatedly goes out. A healthy thermocouple produces a small electric current when exposed to heat. That current keeps the gas valve open. If the thermocouple is stuck in a "cold" state, the valve will close, and the pilot will extinguish. You may find yourself continuously relighting the flame.

2. Heater Shuts Off While Water Remains Hot
After the pilot is lit, the heater should stay on, heating water for the next 20‑30 minutes. If the thermocouple fails, the gas valve will turn off early, even though the water stays hot. You'll see the temperature fall suddenly, and the heater will need relighting every time.

3. Unusual Smells or Lack of Heat
A faulty thermocouple may activate the safety shut‑off, stopping gas flow. This may result in a faint chemical odor from the gas or, worse, no heat at all. Should you detect gas or see the thermostat reading far below the set temperature, inspect the thermocouple.

4. Pilot Flame Flickers or Looks Dim
With a marginal thermocouple, the pilot flame may look weak or flicker. This occurs as the gas valve cycles on and off intermittently. The flame may appear steady, yet the control is unstable.

5. Inconsistent Water Temperature
If the water temperature swings erratically, from hot to lukewarm, the thermocouple could be miscalibrated. Even a slight misalignment can cause the gas valve to open at the wrong times.

6. Physical Wear and Corrosion
Look for visible signs of wear on the thermocouple. If you find corrosion, cracks, or a broken stem, it can’t generate enough voltage. The metal can degrade over time, especially in damp or humid settings.

7. Lagging Pilot Light Response
If you manually turn the pilot flame on and the thermocouple does not respond quickly, 名古屋市東区 エコキュート 交換 it may be stuck. A delayed response usually means the sensor isn’t detecting heat correctly.

8. Error Codes and Warning Lights
Modern gas water heaters may display error codes upon thermocouple failure. A flashing LED or a code on the control panel can point to a "pilot light" or "sensor" issue.

9. Strange Sounds from the Heater
If you hear a rattling or clicking sound when the heater starts, it may indicate the gas valve flickers—another sign of a failing thermocouple.

10. Plumber Re‑lighting Pilot Frequently
If a plumber must relight the pilot repeatedly within a short timeframe, it shows the thermocouple is faulty.

Steps to Replace a Faulty Thermocouple
Turn off the gas supply and wait for the heater to cool
Take out the old thermocouple with a wrench or pliers
Look for corrosion or damage; if present, replace it
Clean the connection spots and pilot flame region
Mount the new thermocouple, aligning the stem to the pilot flame
Reopen the gas, relight the pilot, and verify the heater stays on

If you’re not comfortable working with gas appliances, call a licensed plumber
A quick replacement can avoid gas waste, restore hot water, and keep your home safe