Gas Water Heater Stopped Working? It Might Just Be the High Limit Switch

When your gas water heater suddenly stops producing hot water, it’s easy to assume the worst. Maybe the pilot won’t stay lit, maybe everything looks normal… but the water’s ice cold. Before you call for a replacement or try swapping out random parts, it’s worth checking one small—but important—component: the high limit switch.

This safety device is built to shut things down when the system starts overheating. In many cases, resetting it is enough to bring your water heater back to life. Here’s how to figure out if that’s your issue—and what you can do about it.

🔥 What Is the High Limit Switch?

Also called an ECO (Energy Cut-Off) switch, the high limit switch is a built-in safety feature that kills gas flow to the burner if water temperatures climb too high—usually above 180°F. It’s designed to prevent your tank from becoming a hazard.

When it trips, it tells the gas valve to shut down completely. No flame. No heat. No hot water.

🧊 Signs Your High Limit Switch Has Tripped

These are the most common symptoms that point to a tripped limit switch:

No hot water, even though the pilot was recently working
Tank is full, cold
You try to relight the pilot light, and it won’t stay lit
No signs of leaks, and the gas supply appears fine
Thermostat dial seems normal, but the burner never kicks on

The pilot light symptom throws a lot of people off. You go through the steps—hold the button, light the flame, wait… and the moment you let go? Out it goes. That’s often blamed on a bad thermocouple or gas valve, but a tripped high limit switch can block everything upstream. Until it’s reset, the system won’t cooperate.

✅ How to Reset the High Limit Switch

Step-by-Step Reset:

Access the burner and control assembly.
Remove the metal cover at the base. This usually slides or lifts off.
Look for the reset button.
On many models, it’s a small red button located near or on the gas control valve or thermostat.
Press the reset button.
You may hear or feel a click. That’s the switch resetting. If there’s no resistance or click, the switch may be faulty—or not tripped in the first place.
Reassemble and relight the pilot.
Follow the water heater’s lighting instructions exactly. Hold the pilot button in for the full time listed before releasing.
Turn the gas back on and test.
Once the pilot is stable, turn the thermostat back up and listen for the burner to kick on.

If everything works, you’re back in business. If not—or if the pilot still refuses to stay lit—you may be dealing with a faulty thermocouple, gas valve, or limit switch.

🛠️ Why the Switch Trips

The high limit switch isn’t tripping just for fun. It’s there to prevent overheating, and it’s usually reacting to something upstream. Common causes include:

Faulty thermostat dial sending bad signals
Sediment buildup overheating the bottom of the tank
Improper gas pressure or combustion airflow
Failed or sticky gas control valve
High ambient temperatures around the tank (especially in small closets)

Once it’s tripped, the switch basically says, “That’s it, I’m out,” until someone physically resets it.

🔁 If It Trips Again Soon…

If you’ve reset it once and the heater stays running, great—you may be good for a while.

But if it trips again within a day or two? Don’t keep playing the reset game. That’s your water heater waving a red flag. You could be risking overheating, backdrafting, or worse.

This is the point where it makes sense to call someone in who can test gas pressure, thermostat function, and confirm there’s no dangerous exhaust or flame rollout happening.

🔚 Final Thought

A tripped high limit switch on a gas water heater can be frustrating, but it’s often fixable without a full replacement. If your pilot won’t stay lit and the tank’s not heating, check that reset button before you assume the worst.

Premier Mechanical – www.claimyourcomfort.com – 720.207.6812.