Short answer
This guide interprets the documented codes for the Junkers CerapurComfort ZWBC 25-2 C in the installation and operation manual for the technician, edition 6 720 647 489 (2012/06). The code guides the verification; it does not identify a faulty part by itself. Do not extrapolate the table to other ZWBC, ZWBE, or Cerapur generations without checking the cover and the PCB of the unit.
The manufacturer's table combines codes with internal checks. Here is a summary of what each warning indicates so you can describe it accurately. The checks on gas, electrodes, fan, wiring, PCB, and flue are for qualified personnel; do not open the boiler.
Documented fault codes for ZWBC 25-2 C
| Code | What does the manual indicate? | What can you do? |
|---|---|---|
| A7 | The domestic hot water temperature sensor appears to be faulty. | Note if the domestic hot water fails and communicate the fault code. The sensor and its connection require professional checking. |
| A8 | Communication interrupted. | Check if there is a connected regulator and if the warning appeared after an intervention. Do not tamper with connections. |
| b1 | The encoding connector is not detected. | Requires internal verification; it is not an instruction to remove or reposition connectors. |
| b2 / b3 | Internal data fault. | The manufacturer groups both codes and refers to specialized diagnosis; it does not identify a spare part on its own. |
| C6 | The fan is not working. | Leave the check of the fan and its connections to the professional. |
| CC | The outdoor temperature sensor is not detected. | Indicate if the system has that sensor; the boiler may have different control options. |
| d3 | The external controller TB1 has been activated. | Describe whether there is underfloor heating or external control. The manual mentions internal connections that you should not modify. |
| E2 | The supply temperature sensor appears to be faulty. | Communicate if the warning matches with active heating; do not buy a sensor just for the code. |
| E9 | The temperature limiter of the heat block or the flue gas temperature limiter has been triggered. | Note if the boiler stopped and if the fault code reappears. The cause requires professional diagnosis; do not reset repeatedly. |
| EA | Flame not detected. | Check if the warning appears when trying to start and if heating and domestic hot water are out of service. Gas checks and ignition are not user tasks. |
| F0 | Internal fault. | Request diagnosis; it does not assume that the PCB is the faulty part. |
| F1 | Internal data error. | The manual refers to instructions for the specialist technician. |
| F7 | Flame is detected even though the unit is turned off. | Keep the device turned off and request a review; do not handle gas or electrodes. |
| FA | Flame is still detected after the gas is interrupted. | It is a condition for professional review. Do not attempt to check the gas valve or the duct. |
| Fd | The Reset button has been pressed by mistake. | Check if the button was accidentally pressed. Follow only the user instructions from the corresponding edition. |
Scope of the table: corresponds to the Bosch/Junkers documentation identified below. Codes b2 and b3 share the same description in the original table; this grouping is maintained. The user manual allows for consulting the instructions directed to the owner and the reset procedure for its variant.
If the display does not show one of these fault codes
Take a photo of the display and note the code with its letters and uppercase. Record if it appears when requesting heating, when opening a tap, or when the boiler is stopped; also indicate if it continues to function partially and what pressure the manometer shows. This context helps to differentiate a warning from a cause, but it does not solely determine which component is faulty.
If there is no fault code but heating or hot water is missing, describe the symptom and when it started. Avoid attributing the fault to the pump, valve, sensor, or PCB without measuring and checking the appliance.
When to request a review?
Request assistance if the blockage persists or reappears, if there is a gas smell or abnormal combustion signs, or if you are unsure about the indication. In case of a gas smell, do not operate switches or use flames; move away and follow the emergency instructions from your supplier. To find other guides by model, consult boiler faults by brand and modelThe repair or replacement is decided after confirming the diagnosis and the complete reference of the appliance.
Official documentation: Installation and operating instructions for the technician, CerapurComfort ZWBC 25-2 C, edition 6 720 647 489 (2012/06), section 13.2, printed page 36; and CerapurComfort user instructions for user-directed information. Request boiler inspection.
CerapurComfort ZWBC 25-2 C
Document editing
Applicable to the ZWBC 25-2 C variants indicated by the manufacturer; confirm the PCB of your unit.
CerapurComfort ZWBC 25-2 C
Document editing
User manual for ZWBC 25-2 C; does not replace the technician's instructions.