AO Smith 4 Flashes: High-Temperature Limit (ECO) Trip

Four blinks from the status light, on a loop, usually means your AO Smith tank shut its gas off mid-cycle instead of letting the water keep climbing. That's the Energy Cut-Off (ECO) switch — a safety limit built to stop a runaway thermostat before things get dangerous.

Applies to: AO Smith gas storage tank water heaters with electronic ignition

What it means

High-Temperature Limit (ECO/Energy Cut-Off) Trip — a safety switch shut off the gas because water reached an unsafe temperature. Unlike a normal thermostat cycling on and off throughout the day, the ECO is a manual-reset device: once it opens, the tank stays off until someone resets it. That's deliberate design, not a bug — it forces a look at why the water overheated instead of letting the unit quietly restart on its own.

Most common causes

Thermostat or gas control valve malfunction
Failed ECO switch
Wiring fault

What you can safely check yourself

Turn the gas control knob to OFF and let the tank cool
Follow the ECO reset procedure in your owner's manual (some models have a manual reset button on the gas valve)

When to call a professional

The ECO trips more than once. This is a safety device — a repeat trip means the gas valve or thermostat needs professional replacement, not repeated resetting.

Gas control valves and thermostat components should only be replaced by a licensed plumber or HVAC technician.

What the fix costs

A service call to diagnose why an ECO tripped generally runs $150–$300, based on Angi's and Fixr's water heater repair cost guides. If the gas control valve itself needs replacing — the usual fix for a repeat trip — expect roughly $150–$450 installed, since the ECO is built into the valve assembly on most electronic-ignition models. These are national estimates; a local licensed plumber can give you an actual number after inspecting the unit.

Related codes

All AO Smith codes

Every AO Smith water heater fault code — the full list on one page. If the tank has stopped delivering hot water entirely while this trips, see no hot water from a tank water heater for the wider troubleshooting picture.

Safety. An ECO trip means the tank actually reached an unsafe temperature — treat a repeat trip as a warning sign, not an inconvenience. Don't hold the reset button in or otherwise force the ECO to stay closed; that removes the one safeguard standing between a thermostat fault and scalding water or tank over-pressure.

Sources

AO Smith gas water heater status light / blinking fault code chart (manufacturer documentation)

This site is an independent reference, not a substitute for a licensed plumber or electrician. Gas water heaters can leak carbon monoxide, leak gas, or catch fire if serviced incorrectly. Anything involving the gas line, gas control valve, venting, or main electrical wiring should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.