Lochinvar combi boilers and condensing commercial water heaters display numeric fault codes on the control panel. Code prefixes:
- E-codes — locked-out fault; manual reset typically required
- F-codes — soft fault; auto-clears when condition resolves
- blocking — temporary condition; resumes when satisfied
Common codes
| Code | Meaning | Action |
|---|---|---|
| E02 / E03 | Low water pressure / empty system | Re-pressurize to 12-15 PSI cold; bleed air |
| E04 | Gas valve / ignition failure | Gas supply, igniter, flame sensor, gas pressure |
| E09 | Fan / blower failure | Blower motor, capacitor, wiring, control board |
| E12 | Supply temperature sensor | NTC sensor resistance test; replace if out of spec |
| E29 | High-limit lockout | Overheating; check flow, sensors, control settings |
| E33 | DHW sensor (combi only) | DHW NTC sensor open/shorted; replace |
How to read
- Display shows the active code on the LCD or LED screen
- Press Menu or Info button to see fault history (last 10 events)
- Code persists until manual reset (E-codes) or condition clears (F-codes)
How to reset
- Front-panel reset: press and hold the Reset button 5 seconds
- Power cycle: breaker off 30 seconds for stubborn locks
- Don\'t repeatedly reset without diagnosing — repeated locks indicate persistent fault
Bottom line
Lochinvar fault codes are diagnostic — they tell the contractor where to look. Most resolve with annual service procedures (clear condensate trap, verify sensor resistance, gas pressure). Persistent locks need contractor diagnosis with combustion analyzer and manometer.