AO Smith uses different error code conventions across product families. ProLine Tankless uses two-digit codes; Voltex hybrid uses alphanumeric; Vertex condensing uses C-codes; smart-control units push errors to the iCOMM app. This page covers the most common codes.
Voltex Hybrid Heat Pump error codes
| Code | Meaning | Fix |
|---|---|---|
| E01, E02 | Hot/cold sensor fault | Replace tank temperature sensor |
| E03 | Evaporator sensor fault | Service technician — refrigerant diagnostics |
| E04 | Compressor over-temperature | Clean front-panel air filter (most common cause) |
| E05 | Heat pump fault | Switch to electric-only mode; call AO Smith service |
| F01, F02 | Upper/lower element fault | Test continuity; replace element if open |
| F03 | Thermostat fault | Replace thermostat |
ProLine Tankless (ATI series) error codes
| Code | Meaning | Fix |
|---|---|---|
| 11 | No ignition | Verify gas supply, propane tank not empty, gas valve open |
| 12 | Flame failure | Clean intake filter; check vent termination for blockage |
| 14 | High-temp shutoff (heat exchanger scale) | Descale immediately; recurring code 14 = HX damage |
| 15 | Thermistor fault | Reconnect or replace sensor |
| 29 | Neutralizer fault | Refill/replace condensate neutralizer cartridge |
| 71 | Gas solenoid fault | Warranty-covered — call AO Smith |
| 90 | Combustion abnormal | Vent blockage or insufficient combustion air |
| 92 | Neutralizer life expiring | Replace within 30 days |
Vertex Power Direct Vent error codes
| Code | Meaning | Fix |
|---|---|---|
| C1 | Combustion blower fault | Inducer motor or pressure switch tube — verify tubing first |
| C2 | Pressure switch fault | Often silicone tube has slipped off inducer. Reattach. |
| C3 | Ignition failure | Replace igniter assembly (~$50) |
| C4 | Flame sensor fault | Clean flame rod with fine steel wool |
iCOMM app errors
AO Smith's iCOMM (Voltex, Signature Premier with smart control) pushes errors to the mobile app rather than displaying on the unit. App messages are plain-language ("Leak detected", "WiFi lost", "Heat pump fault — switching to electric backup"). Open the iCOMM app Diagnostics page for full details and recommended actions.
When to call a pro vs DIY
DIY-friendly: C2 (silicone tube), C4 (flame rod clean), Voltex E04 (filter clean), most "sensor failed" codes.
Service tech: Voltex E03/E05 (refrigerant work), ProLine Tankless 71 (gas solenoid).
Bottom line
For full troubleshooting context see our troubleshooting hub. For warranty claims see the warranty page.