AO Smith ECT66 water heater Parts

The most common water heater problem is a loss of hot water or not enough hot water, usually caused by sediment buildup on the heating elements or a failed thermostat. On the Ao Smith ECT66 electric water heater, the first parts we check are the heating element 100108283 and the thermostats.

What you will typically notice first

• Hot water runs out faster than it used to
• Water temperature swings from hot to lukewarm
• Popping or rumbling noises (sediment heating up and breaking loose)
• Higher electric bills from longer heat cycles
• Water is too hot or not hot enough (thermostat control issue)

Quick checks we recommend (electric models like ECT66)

1. Confirm power: Check the breaker and that the unit is receiving power.
2. Look for a tripped reset: Many electric water heaters have a high-limit reset on the upper thermostat.
3. Test the heating circuit: Use a multimeter to check for continuity and proper voltage at the elements and thermostats.
4. Inspect for sediment symptoms: Noise and reduced capacity often point to scale buildup.
5. Check for leaks: Look at fittings, the drain valve area, and around access panels.

If you are ordering parts, use the ECT66 parts list first, or search by model on Sears PartsDirect.

Common causes and the parts that usually fix them

Symptom	Most common cause	Parts often involved for ECT66
No hot water	Failed upper thermostat or upper element	Thermostat, element
Not enough hot water	Lower element scaled out or failed	Element
Water too hot or too cold	Thermostat out of calibration or stuck	Thermostat
Rumbling/popping	Sediment buildup in tank	Maintenance (flush), element may be damaged

Why it matters

When sediment insulates the element, the heater runs longer, costs more to operate, and can overheat components. Catching an element or thermostat problem early helps restore normal recovery time and reduces stress on wiring and terminals.

Last updated: February 2026

On the Ao Smith ECT66 electric water heater, resetting usually means restoring power and pressing the high-limit reset (ECO) button behind the upper access panel. If it trips again, a failed thermostat or heating element is commonly causing overheating.

Reset steps (electric water heater)

• Turn OFF the water heater breaker (240V) and confirm power is off.
• Remove the upper access panel and insulation.
• Press the red reset button on the upper thermostat (you should feel a firm click if it was tripped).
• Reinstall insulation and the access panel.
• Turn the breaker ON and wait 30 to 60 minutes for recovery.

If the reset keeps tripping

A repeated trip means the water is overheating or the control is sensing unsafe temperature.

Common causes to check:

• Thermostat contacts stuck closed (upper or lower thermostat)
• Shorted or grounded heating element
• Loose/burned wiring at terminals
• Incorrect thermostat temperature setting
• Missing insulation or access cover not installed correctly (can affect sensing)

Helpful parts for this model include the thermostat 100109846, thermostat 100110039, and heating element 100108283.

Quick troubleshooting guide

Symptom	Most likely issue	What we recommend
Reset trips within minutes	Shorted element or wiring	Test element for ground, inspect terminals
Water is scalding hot	Thermostat stuck closed or mis-set	Lower setting, replace thermostat if needed
Lukewarm water, no trip	One element not heating	Test elements for continuity

Why it matters

The reset (ECO) is a safety device that shuts the heater down when water temperature gets too high. Resetting it without fixing the cause can lead to repeated shutdowns and inconsistent hot water.

You can order ECT66 replacement parts from the parts list for your model, or search by model number on Sears PartsDirect.

Last updated: February 2026

Most Ao Smith electric water heaters, including model ECT66, have a typical life expectancy of 10 to 12 years. With consistent maintenance (flushing sediment and protecting the tank from corrosion), it’s common to reach 12 to 15 years before major repairs or replacement make more sense.

Typical lifespan and what changes it

A water heater’s tank life is mainly about corrosion control and sediment buildup. These factors have the biggest impact:

• Water quality: hard water speeds up scale on the heating elements
• Maintenance: regular flushing reduces sediment and overheating
• Anode rod condition: a worn anode rod lets the tank rust faster
• Temperature setting: higher temps increase stress and scale
• Usage level: heavy daily demand increases cycling and wear

Maintenance that extends life (and what parts are involved)

If you want the longest service life from an ECT66, these are the most effective, practical steps:

• Flush the tank periodically to remove sediment
• Inspect and replace the anode rod when it’s heavily depleted (a key tank-protection part)
• Check for overheating signs (scalding water, popping sounds, tripped reset)
• Test thermostats if temperatures swing or recovery is slow
• Replace scaled or failed heating elements to restore normal heating and reduce strain

Helpful model-related parts you can match by symptom include the anode rod 100109594, element 100108283, and thermostat 100109846.

Quick guide: what to expect by age

Water heater age	What’s normal	What we recommend checking
0 to 5 years	Fast recovery, stable temps	Basic flushing routine
6 to 10 years	More sediment noise possible	Anode rod, elements, thermostats
10 to 15 years	Higher leak risk, slower recovery	Tank condition, corrosion signs
15+ years	End-of-life is common	Plan replacement if repairs stack up

Why it matters

Once the tank starts corroding internally, repairs like elements and thermostats can restore heat, but they cannot stop a weakened tank from eventually leaking. Replacing the anode rod on time is the single best way to protect the tank and extend overall life.

For replacement parts for your Ao Smith ECT66, use the parts list for this model or search by model number on Sears PartsDirect.

Last updated: February 2026