Equipment error code

AO Smith code E04

E04 — lower heating element fault. Abnormal electrical condition detected on the lower element circuit.

Equipment: water heater
Brand: AO Smith
Source checked: 2026-03-01

What this code means

E04 — lower heating element fault. Abnormal electrical condition detected on the lower element circuit.

Source: AO Smith Voltex Heat Pump Water Heater Owner's Manual — Diagnostic Codes · checked 2026-03-01

Which models show it

AO Smith electric and Voltex heat pump tanks with dual-element diagnostics.

What is actually happening

Hot water runs out quickly; E04 on display. Upper may work alone with poor capacity.

Is it safe to keep running?

Short showers only until repaired — tank stratification hides problems.

Shut it down when

Tripping breaker, leak at element port, or burning smell.

What a homeowner can safely check

Single breaker reset.
Listen for popping from tank — sediment can stress elements.
Note age of tank for replace-vs-repair talk.

When to stop

Leak at lower element threads.
Breaker will not stay on.

Likely causes ranked

1. Failed lower element
How a tech confirms: Resistance test after de-energizing.
Typical repair: $225–$475 · Water Heater Replacement cost guide
2. Lower thermostat failure
How a tech confirms: Continuity and calibration test.
Typical repair: $165–$350 · Water Heater Replacement cost guide
3. Heavy sediment insulating lower element
How a tech confirms: Drain inspection; flush or replace tank if scale-bound.
Typical repair: $200–$1,400 · Water Heater Replacement cost guide
4. Loose or burned wire at element
How a tech confirms: Torque and visual at junction.
Typical repair: $125–$285 · Water Heater Replacement cost guide

Is this the end of this unit?

Dual element failures on tanks past 12 years with rust-colored flush water — replace tank.

How to clear the code

Breaker reset once; persistent E04 needs element service.

Why clearing is not fixing it: Electrical fault on lower circuit remains until parts replaced.

Which trade to call

Call a licensed plumber who works on water heater equipment. Gas, refrigerant, and combustion faults are not general handyman jobs.

How to find a good plumber

Before you sign a contract for this job, use our guide on how to find a good plumber: verify the licence at the state board, compare three itemized quotes on the same scope, and put permit responsibility and change-order rules in writing.

Read the plumber hire guide Check if your quote is fair Verify licences by state

More codes from this brand

Symptom guide: No Hot Water

FAQ

E04 meaning AO Smith?

Lower element fault.

E03 and E04 together?

Both elements or board issue — service visit required.

Flush fix E04?

If sediment caused overheat damage, flush may not save element.

E04 repair price?

$125–$1,400 from wiring to new tank.

Voltex heat pump show E04?

Backup electric lower element can trip E04 independent of heat pump mode.

Source

Source — AO Smith Voltex Heat Pump Water Heater Owner's Manual — Diagnostic Codes. Checked 2026-03-01.