HVACopediaBosch boiler error codes
19 codes with causes and test steps.
| Code | Meaning | Severity |
|---|---|---|
| A7 | DHW temperature sensor fault | Medium |
| A8 | Communication fault | Medium |
| b1 | Code plug not detected | Medium |
| b2/b3/b4/b5/b6 | Internal data error | Medium |
| b7 | Burner control fault | Medium |
| C6 | Fan not running | High |
| d3 | High limit / temperature limiter circuit open | High |
| d5 | External supply temperature sensor fault (low-loss header) | Medium |
| E2 | Supply temperature sensor fault | High |
| E3 | Additional supply temperature sensor fault | Medium |
| E9 | Safety high limit or flue gas limiter tripped | High |
| F0 | Internal fault | Medium |
| F1 | Internal data error | Medium |
| F7 | Flame detected with burner off | High |
| Ad | DHW tank temperature not detected | Medium |
| CC | Outdoor temperature sensor not recognised | Low |
| EA | No flame detected | High |
| FA | Flame detected after gas shut off | Critical |
| Fd | Reset button pressed by mistake | Low |
Models covered
ZBR21-3AZBR28-3AZBR35-3AZBR42-3A
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.