View Junkers faults by model and generation
EA is associated with flame detection, E9 with the flow high-limit thermostat, and C6 with the differential pressure switch. Find out what each Ceraclass signal means, which causes to distinguish, and what to observe if hot water or heating fails.
Junkers Ceraclass Excellence symptoms and faults
EA: no flame detectedEA means the appliance has not detected a flame.
Diagnosis distinguishes the gas supply and pressure, mains connection, ignition and ionisation electrodes, and their wiring.
Source: Bosch/Junkers 6 720 613 279 (2010/04), table 28 · page 57.
E9: flow high-limit thermostat activatedE9 indicates that the flow STB high-limit thermostat has activated.
Checks cover system pressure, temperature sensor, pump circulation, control-board fuse and bleeding.
Source: Bosch/Junkers 6 720 613 279 (2010/04), table 28 · page 57.
C6: differential pressure switch does not closeC6 describes a missing closure signal from the differential pressure switch.
The manufacturer says to check the pressure switch and flue duct; it does not directly attribute this code to a failed fan.
Source: Bosch/Junkers 6 720 613 279 (2010/04), table 28 · page 57.
The hot water works, but the heating does not.The ZWC provides instantaneous hot water and gives it priority over heating.
Note whether the radiators start heating again when the tap is closed, whether a code appears, and whether one or both services are affected. These details help distinguish an interruption during a DHW demand from a fault that persists.
Source: Bosch/Junkers 6 720 613 279 (2010/04), type list and appliance description; ZWC design · pages 6, 7, 9.
Lockout and the code cannot be readThe Ceraclass displays faults on its screen.
A clear photo of the panel and the full appliance reference help identify the applicable table without mistaking an unreadable signal for a different code.
Source: Bosch/Junkers 6 720 613 279 (2010/04), types on p. 6, faults in section 7.12 and table 28 · pages 6, 34, 57.
What to observe: identify the full model, record the panel indication and distinguish whether hot water, heating or both are failing. The indication guides the checks; the diagnosis determines the repair.
A code indicates the condition detected by the boiler, but by itself it does not confirm the specific cause or identify a part to replace.
Fault codes
| Code | Meaning given in the manual |
|---|---|
| A7 | Domestic hot water temperature sensor faulty (ZWC). |
| A8 | BUS communication interrupted. |
| A9 | Domestic hot water temperature sensor incorrectly fitted (ZWC). |
| b1 | Coding plug not detected. |
| C1 | Differential pressure switch activated during operation. |
| C4 | Differential pressure switch does not open at rest. |
| C6 | The differential pressure switch does not close. |
| CC | The outdoor temperature sensor is not detected. |
| d3 | Jumper 161 at ST8 not detected. |
| d4 | Excessive temperature. |
| d7 | Gas valve faulty. |
| E2 | Flow temperature sensor faulty. |
| E9 | The STB on the flow line has been activated. |
| EA | Flame not detected. |
| F0 | Internal fault. |
| F7 | Flame is detected even though the unit is turned off. |
| FA | Flame continues to be detected after the gas is shut off. |
| Fd | The reset button was accidentally held down for more than 30 seconds. |
If you see another code, provide the display text and the full model shown on the rating plate so the relevant documentation can be found.
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Frequently asked questions
Table 28 describes it as no flame detected. It lists several checks involving the supply, ignition, flame detection and connections; the code alone does not identify the specific cause or a spare part.
No. E9 indicates that the flow STB high-limit thermostat has activated. The manual calls for several conditions to be checked, including system pressure, sensor, pump, fuse and bleeding. Diagnosis must distinguish between them.
No. C6 describes the differential pressure switch not closing. The documentation says to check the pressure switch itself and the flue duct before assigning a cause or deciding on a repair.
Give the exact model from the nameplate, say which service works, whether a code appears on the display, when it happens and whether the fault is constant. The symptom alone does not prove which component is affected.
If you smell gas: follow the safety instructions in the manual: ventilate the area, do not operate switches or use flames, leave the premises, and call the gas supplier from outside. Close the gas valve only if you can do so without risk.
Junkers boiler spare parts
These categories let you browse the catalogue by part type and brand; they do not guarantee compatibility with the ZWC 35/35-3 MFA M. Check the variant and part reference against the specific product listing before choosing a spare part.
- Junkers plate heat exchangers
- Junkers electronic control boards
- Junkers gas valves
- Junkers pumps
- Junkers extractors
Boiler manuals
- Bosch/Junkers Ceraclass Excellence user instructions (6 720 613 280, 2010/04).
- Bosch/Junkers installation and maintenance instructions (6 720 613 279, 2010/04): model types, p. 6, and fault table 28, p. 57.
Ceraclass Excellence
Document editing
Include ZWC 35/35-3 MFA M. Check the full model on the cover.
Ceraclass Excellence
Document editing
Document for the technician. List of types on page 6 and table 28 of faults on page 57.