A. O. Smith Water Heater Error E04 – Causes & Fix
The electronic thermostat can't power the upper element; the lower one still works, so hot water runs short.
Safety first · Consult a professional
Everything behind the access panels runs on 240 volts. Turn the heater's breaker off and verify the power is dead before you open a panel or touch a meter lead to a terminal. Water inside may still be hot when you drain the tank to change an element – let it cool or use gloves and a hose to a safe drain.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
- Hot surfaces and hot water can cause burns. Let the appliance cool down first.
At a glance
Severity: Low
- Meaning
- Upper Heating Element Circuit Failure
- Typical repair cost
- $25–$500
- DIY difficulty
- Moderate
On A. O. Smith residential electric water heaters with the Electronic Thermostat (ET) and Energy Saver Module (ESM), E04 means the ET has found a fault in the upper heating element circuit. The heater keeps going in a limited mode – the manual notes the lower element is still operable – so you usually get some hot water, just less of it and with slower recovery. A. O. Smith's corrective steps are to switch off the breaker, measure the element circuit for 5–25 ohms, inspect the wires at the elements and the ET for damage, and replace the ET if the element and wiring test good. By far the commonest finding is a burned-out upper element, frequently after the heater was powered before the tank was completely full.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Electric models with Energy Saver Module (ESM) display | E04 | Shown with the flashing alert icon; the element icon may indicate only one element working. |
| Electronic Thermostat (ET) diagnostic LED | 4 flashes | Four red half-second flashes and a pause, repeating while the fault is present. |
| ESM unplugged / override mode | 4 flashes | With the module disconnected the ET still runs the heater from its setpoint knob and reports the fault only by LED. Don't confuse it with 5 flashes (E05), which is the lower element. |
Symptoms
- ESM shows E04 with the alert icon flashing
- ET diagnostic LED gives four red flashes, then a pause
- Showers run lukewarm or cold much sooner than before
- Tank takes much longer to recover after heavy use
- Fault appeared right after installation or after the tank was drained and refilled
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Upper heating element burned out (open circuit) from age, scale or sediment
- Upper element dry-fired – powered before the tank was full of water after installation or draining
- Loose, burned or corroded wire connection at the upper element terminals
- Relay or output on the Electronic Thermostat failed
- Damaged wiring between the ET and the upper element
Fix it step by step
Switch off and verify
Turn off the double-pole breaker for the water heater and confirm with a tester that no voltage reaches the heater before opening anything.
Tools: Multimeter
Inspect the upper compartment
Remove the upper access panel, fold the insulation aside and look for scorched wires, melted insulation or a discolored terminal on the element. Burn marks point to a loose connection that must be repaired along with the element.
Tools: Screwdriver, Flashlight
Measure the element
Disconnect one wire from the upper element and measure across its two terminals: A. O. Smith expects 5–25 ohms. An open reading (no continuity) means the element is dead. Also check from each terminal to the tank – any reading there means the element is shorted to ground and must be replaced.
Tools: Multimeter, Screwdriver
Replacing the element
Close the cold supply, open a hot tap, and drain the tank below the element with a hose on the drain valve. Unscrew the element with an element wrench, fit a new one of the same voltage and wattage as the data plate with a new gasket, then refill.
Tools: Towels & shallow pan, Gloves
Refill completely before power
With a hot tap open, let water run full for at least three minutes until no air sputters out – A. O. Smith's manual stresses this to prevent dry-firing the new element. Only then restore power at the breaker.
If E04 persists, suspect the ET
When the element measures within 5–25 ohms and the wiring is sound but E04 remains, the Electronic Thermostat is the likely fault. A licensed plumber or appliance technician can confirm and replace it.
How to reset E04
- Fix the cause (element, wiring) with the breaker off.
- Make sure the tank is completely full and air is purged from a hot tap before restoring power.
- Turn the breaker back on; the code should clear once the ET sees a healthy upper element circuit.
- If E04 remains with a good element and wiring, the Electronic Thermostat needs replacing.
Where the parts are
- 1Flue
- 2Fan
- 3Heat exchanger
- 4Ignition electrode
- 5Gas valve
- 6Circulation pump
- 7Expansion tank
- 8Pressure gauge
- 9Temperature sensor
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace upper element yourself (element, gasket, element wrench) | Yes | $25–$60 |
| Element replacement by a plumber | No | $180–$350 |
| Repair burned terminal or wiring | No | $120–$250 |
| Replace Electronic Thermostat (ET) | No | $250–$500 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call a licensed plumber or appliance technician if you're not comfortable testing 240-volt circuits or draining the tank, if you find burned wiring, or if E04 stays after the element tests good. A new heater that showed E04 right after installation may have been dry-fired, which A. O. Smith treats as an installation error rather than a warranty defect.
Frequently asked questions
Can I still use the water heater with E04?
Yes, in a limited way – the lower element keeps working, so you'll have some hot water but less capacity and slower recovery. Plan the repair soon rather than relying on one element long term.
Why did E04 appear right after my new heater was installed?
The most common reason is that power was turned on before the tank was completely full, burning out the upper element within seconds. A. O. Smith treats a dry-fired upper element as an installation error, so talk to the installer.
What's the difference between E04 and E05?
E04 is the upper element circuit and E05 the lower one. The test is the same (5–25 ohms), but the element you replace and the symptoms differ – with E04 the top of the tank heats poorly.
Which replacement element should I buy?
Match the voltage and wattage printed on the heater's data plate. A higher-wattage element can overload the wiring and breaker, and a wrong voltage rating either won't heat properly or will burn out.
Sources
- Official A. O. Smith user documentation and support pages (facts only; wording is our own)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy