The Accelera 300 E uses a different fault-code system than Tempra Plus. Display shows alphanumeric codes for heat pump and resistance backup faults.
Common Accelera codes
| Code | Meaning | Action |
|---|---|---|
| HP-1 | Heat pump compressor fault | Verify ambient 45-95°F; reset; tech support if persists |
| HP-2 | Compressor over-current | Breaker check; ambient extreme; tech support |
| SE-1 | Tank temperature sensor fault | NTC sensor test; replace |
| SE-2 | Ambient temperature sensor | NTC sensor test; replace |
| CO-1 | Condensate drain blocked | Clear drain trap; verify gravity drainage or pump |
| AM-1 | Ambient temperature out of range | Move unit OR install ducting kit; reset |
| HE-1 | High ambient / high tank temperature | Check ventilation; air space 700+ cu ft |
Diagnostic sequence by symptom
Slow recovery / heat pump not running
- Verify mode is "Heat Pump" or "Hybrid" — not "Vacation" or "Standby"
- Check ambient temperature — below 45°F triggers electric backup, above 95°F triggers thermal lockout
- Inspect air filter — clogged filter shuts down heat pump mode
- Verify air space — closet without louvered doors traps heat
- Inspect condensate drain — blocked drain triggers safety shutdown
Code CO-1 (condensate blocked)
- Inspect condensate trap and drain hose for visible obstruction
- Pour water into the condensate pan — verify drainage
- If gravity drain, verify slope away from unit
- If condensate pump, verify pump operation and outlet hose clear
- Clean trap with vinegar to dissolve any biological growth
Code HE-1 (high temperature)
- Verify 700+ cu ft air space around unit
- If closet install, verify louvered doors with 240+ sq in ventilation
- Verify exhaust isn\'t recirculating into intake
- Consider Stiebel ducting kit for installs without adequate room air
Code HP-1 / HP-2 (compressor)
- Compressor is sealed system — homeowner can\'t service
- Compressor warranty: 5 years
- Call Stiebel tech support immediately — diagnosis often identifies low refrigerant charge or compressor failure
- EPA-certified HVAC tech required for compressor work
Reset
- Most Accelera faults clear automatically when condition resolves
- Manual reset: press reset button on control panel
- Hard reset: breaker off 60 seconds, then on
- Compressor faults: don\'t repeatedly reset; call tech support to avoid damaging compressor
Bottom line
Accelera codes are mostly self-diagnosing. Sensor faults are homeowner-serviceable (with skills); compressor faults are warranty replacement under 5 years or HVAC technician work. Stiebel tech support is excellent for Accelera-specific guidance.