Heating element failure is the most common AO Smith electric water heater service item. Elements last 6–10 years depending on water hardness. Replacement is a 60-minute DIY at $30–$60 parts cost.
Symptoms by which element failed
- Upper element failed: no hot water at all
- Lower element failed: hot at first then quickly lukewarm
- Both failed: no hot water + breaker trips (rare — usually lightning or sustained over-voltage)
AO Smith element part numbers
| Element | AO Smith part |
|---|---|
| Standard 4500W (Signature 100, ProMax electric, ProLine 30G) | 9000-666015 or universal 4500W 1" NPT screw-in |
| High-recovery 5500W (variants) | 9000-666025 |
| Voltex backup element (4500W) | 9000-666035 (specialized) |
| Conservationist 6G lowboy (1440W 120V) | Specialty — verify by model |
How to test which element failed
Need a multimeter set to ohms.
- Shut off power, verify with voltage meter
- Remove access panel covering the element
- Disconnect element wires from terminals
- Set multimeter to 200 ohm range, touch probes to terminals
- Reading 10–16 ohms = good; 0 or OL = failed; 1–9 ohms = shorted
Replacement procedure
- Shut off power, verify
- Shut off cold inlet
- Open hot faucet in house
- Drain tank to below the element you're replacing (full drain for lower element)
- Remove access panel and insulation
- Disconnect element wires
- Unscrew element with 1-1/2" element wrench ($15 at any hardware store)
- Pull element straight out with old gasket
- Install new element with fresh gasket, hand-thread, torque ~25 ft-lbs
- Reconnect wires
- Refill tank — open cold inlet, run hot faucet until steady
- Restore power AFTER tank is full
Common mistakes
- Powering up before refilling — destroys new element in seconds. #1 mistake.
- Using regular socket instead of element wrench — rounds the hex
- Cross-threading — hand-thread first, restart if you feel resistance early
- Reusing the gasket — single-use; guarantees a slow leak
Bottom line
Element replacement is ~$50 in parts + an hour vs $200–$350 for a service call. Element wrench is the only specialty tool. For other parts see our AO Smith parts hub.