American Water Heater 24 inch thermocouple
Use on short gas models after confirming pilot flame and millivolt output.
$8-$15
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American Water Heater Error Codes
American Water Heaters is a subsidiary of A.O. Smith and shares manufacturing with State and A.O. Smith brands. The controls and error codes are nearly identical across all three brands.
Gas Models — LED Flash Codes
American Water Heater gas models (ProLine, Glasslined, Commercial series) use an LED status indicator on the gas valve body:
| Flash Code | Meaning | Fix |
|---|---|---|
| 1 flash | Normal operation | None — system OK |
| 2 flashes | Low thermopile voltage | Clean thermocouple, check pilot flame |
| 3 flashes | Pressure switch fault (power vent models only) | Check blower, hoses, vent |
| 4 flashes | Temperature limit exceeded | Reduce setpoint, check T&P valve |
| 5 flashes | Thermal switch / sensor fault | Replace gas control valve |
| 6 flashes | Gas valve internal fault | Replace gas control valve |
| 7 flashes | Pilot not proving | Relight pilot, replace thermocouple |
| Continuous ON | Power fault / flame without pilot | Gas valve failure |
Electric Models — Digital Display Codes
American Water Heater electric models with digital controls (ProLine Specialist, Marathon series):
| Code | Meaning | Action |
|---|---|---|
| E1 | Upper heating element fault | Test, replace element |
| E2 | Lower heating element fault | Test, replace element |
| E3 | Upper thermostat fault | Test or replace thermostat |
| E4 | Lower thermostat fault | Test or replace thermostat |
| E5 | High limit (ECO) tripped | Reset red button, find cause |
| E6 | Control board fault | Replace electronic thermostat/board |
Most Common American Water Heater Faults
2 Flashes — Low Thermopile Voltage
The pilot flame heats a thermopile (multiple thermocouples in series) that generates 250–750 mV to power the gas valve electronically. When this voltage drops below threshold:
- Pilot may appear lit but the gas valve won’t open for main burner
- Water goes cold even though pilot is visible
Fix:
- Ensure pilot flame is the correct size — should engulf the tip of the thermocouple about 3/8”–1/2”
- Clean thermocouple tip with fine steel wool
- Check that the thermocouple connection at the gas valve is hand-tight + 1/4 turn
- If millivolt reading is under 200 mV with pilot lit for 2+ minutes, replace the thermocouple/thermopile
7 Flashes — Pilot Not Proving
The gas valve controller doesn’t sense a pilot even when you’re trying to light it.
Step-by-step relight:
- Set control knob to OFF, wait 5 minutes
- Set to PILOT, push knob in, hold down
- Use piezo button or lighter to light pilot through access opening
- Hold knob for 45–60 seconds after lighting
- Slowly release — pilot should hold
If pilot won’t hold: thermocouple failure. Cost: $10–15 at hardware store.
E5 — High Limit Tripped (Electric)
The ECO (Energy Cut Off) is a manual reset thermal fuse behind the upper access panel:
- Turn off breaker
- Remove access panel and push insulation aside
- Press the small red button firmly — you’ll feel/hear a click when it resets
- Restore power
Investigate why it tripped: failed thermostat letting element run continuously is the usual cause.
American Water Heater Thermocouple Replacement
Most American Water Heater gas models use a standard 24” or 36” universal thermocouple:
| Part | Source | Cost |
|---|---|---|
| 24” universal thermocouple | Hardware store (Rheem, Honeywell compatible) | $8–15 |
| 36” for tall units | Hardware store | $10–18 |
| OEM thermocouple | AWH parts online | $15–25 |
Need Replacement Parts?
Before ordering, match the water-heating part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Thread the thermocouple into the gas valve finger-tight plus 1/4 turn — never overtighten, as the fitting is soft brass.
Replacing a Gas Control Valve
If you’re seeing codes 5, 6, or “continuous on” after ruling out external causes, the gas control valve has failed. American Water Heater uses a combination thermostat/gas valve that is a single replacement unit:
- Turn off gas at the shutoff valve upstream
- Drain tank partially (below gas valve level)
- Disconnect the thermocouple, pilot tube, and main gas line
- Unscrew the valve from the tank (large wrench needed)
- Apply pipe thread sealant to new valve
- Reinstall in reverse order
Cost: $60–120 for OEM, $40–60 for aftermarket.
Warranty Note
American Water Heater products typically come with 6-year (basic) or 12-year (premium) tank warranties. If your unit is within warranty, contact AWH at 1-800-999-9515 before paying for parts — they may cover components or full replacement.