Boilers and water heaters, Junkers
Junkerserror codes: complete table of boiler and water heater faults
If your Junkers has stopped and is displaying a code, here you'll find error codes Junkers explained in one place: what each one means, which models it appears on, and what to check. For the most common codes, you'll find a complete guide with step-by-step diagnostics and replacement parts.
The information is based on the Junkers ( BoschGroup) professional troubleshooting manual, which covers conventional, low NOx, and condensing boilers, as well as miniMAXX, HydroPower-Plus, Celsius, and miniMAXX Excellence water heaters. We explain it in our own words and add what we've learned selling spare parts.
The four most searched codes
- EA: No flame detected. It's almost always a lack of gas, but if you see a flame and it still comes out, it's the ionization electrode.
- E9: Overheating. Check pressure, radiators, air and pump before the limiter.
- A7 / E2: Temperature probes. Often it's the cable or the connector, not the probe.
- C6 / C4: pressure switch and flue gas evacuation. In condensing systems, C6 is the fan.
Junkers error code table
| Code | What does it mean | Models | Solution |
|---|---|---|---|
| EA | No flame detected: lack of gas, spark or ionization failure | All boilers and water heaters with display | View guide |
| E9 | Overheating: the temperature limiter has been activated | All | View guide |
| A7 | Hot water probe (in water heaters, outlet probe) | Boilers and heaters | View guide |
| E2 | Heating flow sensor (in some heaters, inlet sensor) | Boilers, HydroPower-Plus, miniMAXX Excellence | View guide |
| E4 | Cold water probe or solar inlet NTC | Cerapur Acu, Eur | View guide |
| Ad | The accumulator probe is not detected | Boilers with storage tank | View guide |
| A9 | Hot water probe incorrectly installed or measuring incorrectly | Ceraclass Excellence, Cerapur Acu, heaters | View guide |
| C6 | Pressure switch does not close (in condensation: the fan does not work) | Boilers and heaters | View guide |
| C4 | Pressure switch does not open at rest | Sealed boilers and water heaters | View guide |
| C1 / C2 | Pressure switch opens during operation | Sealed boilers (C1), water heaters (C2) | View guide |
| C7 | No fan speed signal | EurMFA | View guide |
| F7 | Detects flame when it shouldn't (appliance switched off or before the gas is turned on) | All | View guide |
| FA | It continues to detect a flame after turning off the gas | All | View guide |
| F0 / F1 / E0 | Internal error of the electronic board or data | All | Soon |
| b1 / b2 / b3 | Encoder connector or internal data error | Boilers | Soon |
| A3 / A4 / A2 / A6 | Smoke sensors, smoke outlet through the draft diverter or the chamber | Natural draft boilers and water heaters | Soon |
| AA | Excessive temperature difference or insufficient flow rate (cal) | Eur, Ceraclass Midi | Soon |
| A8 / AC | Communication with the regulator or module interrupted | Boilers with regulation | Soon |
| DC | The outdoor temperature probe is not detected | Boilers with external probe | Soon |
| d3 | The thermostat jumper is missing or the external controller has been activated | Boilers | Soon |
| d4 / d5 / d7 | Excessive temperature, external drive probe or regulating valve | Ceraclass Excellence, Cerapur | Soon |
| E1 | Over-temperature of the outlet water (more than 85 °C) | Heaters | View guide |
| AC | Water flow rate above maximum | HydroPower-Plus, Euromaxx (turbine) | View guide |
| EC | Intermittent ionization failure | miniMAXX Excellence | View guide |
| Fd | Reset key pressed by mistake or for too long | All | Press reset again |
| US | Electrical voltage below 185 V | EurMFA | Review your diet |
| P1, P2, P3… | Initially, it's not a breakdown | Eur | Wait |
The same code can mean slightly different things depending on the appliance family. That's why in each guide we separate what the manufacturer indicates for each model.
What model of Junkers do I have?
Locate the nameplate: it's usually on the bottom of the case or behind the front cover. The most common references are:
- Condensing boilers: Cerapur (ZWB…-2C), Cerapur Comfort (ZWBC…-2C), Cerapur Excellence (ZWBE/ZSBE…-2A) and Cerapur Acu (ZWSB…-3A).
- Low NOx and sealed boilers: Ceraclass Excellence (ZSC/ZWC…3 MFA/MFK), Cerastar (ZWN 24-7 MFA), Ceraclass Midi (ZW 24 AE/KE), Euromaxx (ZC/ZWC…MFK/MFA), Eurostar Acu-Hit (ZWSE 23-4 MFK, ZWC 28-4 MFA).
- Boilers without screen: Eur(ZW…-1) and Ceraline Acu (ZWSE 28-5 MFK/MFA).
- Heaters: miniMAXX (WR-2), miniMAXX Excellence (WTD…KME), HydroPower-Plus (WTD…KG) and Celsius / Celsius Plus (WT…, WTD…).
Junkers without a display: how to read fault codes
Euronline: LED combinations
The Eurline indicates a fault by illuminating the red LED along with one or more green LEDs. You can find a complete explanation in the fault light Eurline.
- Red + 2nd green: overtemperature, the limiter has cut out (equivalent to E9).
- Red + 3rd green: there is a spark but no flame is detected (equivalent to EA).
- Red + 4th green: detects flame without spark: false flame signal (equivalent to F7).
- Red + 2nd and 5th green: poor gas evacuation (pressure switch, fan, AGÜ probe). See pressure switch guide.
- Red + 3rd and 5th green: Primary NTC open or shorted. See probe guide.
- Red + 4th and 5th green: Hot water NTC open or shorted.
- Red + 5° green: slight overheating (plate heat exchanger or primary NTC).
Ceraline Acu: pilot flickers
Full explanation in the Ceraline Acu blink guide .
- 1 blink: no flame detected (EA).
- 2 blinks: temperature sensors interrupted or shorted.
- 3 blinks: the limiter has acted on the outbound (E9).
- 4 blinks: pressure switch (MFA version) or smoke outlet (MFK version).
- 5 blinks: internal fault: connections, ignition cables or printed circuit board.
Is your Junkers water heater not turning on?
If your water heater won't turn on, clicks but doesn't ignite, or shuts off, the problem is usually with the water, batteries, diaphragm, or gas. We'll go through these in order in our water heater Junkers won't turn on."
What appears on the screen is not a malfunction
Many Junkers display symbols that may seem alarming, but they are actually normal: the key lock is active, the inspection is required, the siphon filling program activates after switching on a condensing boiler, the purge functionactive, gradient monitoring (heating stops for two minutes because the temperature rises too quickly), the floor drying function, thermal disinfection , or the pump is in anti-blocking safety mode. None of these require replacement.
Where can I buy Junkersspare parts?
At ElectroCholo, we have over 400 spare parts for Junkers: electrodes, NTC probes, pressure switches, fans, pumps, limiters, and circuit boards. You can see them all in spare parts section Junkers or contact us with the reference number from your nameplate.
Frequently Asked Questions
Can I clear the error code by pressing reset?
You can reset once or twice to rule out a one-off failure. If the code returns, there's a cause to find; looping through resets won't solve it.
Are Junkers part numbers the same as Boschpart numbers?
Junkers belongs to the Bosch Group, and many boilers share electronics, so quite a few part numbers are the same. Even so, always double-check with the exact model.
Which codes indicate that I should call a technician now?
Any related to smoke evacuation (A3, A4, C1, C6) or flame control (F7, FA) if it occurs repeatedly. These relate to combustion safety.
Important notice
This article is a guide based on the manufacturer's technical documentation and our experience as a spare parts store. It is not a substitute for professional diagnosis. Every appliance and every installation is different, and the same error code can have different causes.
Any work on the gas circuit, combustion, or flue system must be carried out by a qualified installer, in accordance with the Technical Regulation for the Distribution and Use of Gaseous Fuels (RD 919/2006) and the Regulation on Thermal Installations in Buildings (RITE). Manipulating these elements without the necessary qualifications can be dangerous and will void the appliance's warranty.
The decision to purchase a replacement part based on this information is the sole responsibility of the customer. ElectroCholo is not liable for incorrect diagnoses or damage resulting from improper installation. Electrical and electronic parts that have been assembled or installed are non-returnable if the fault turns out to be something else, in accordance with our general terms and conditions.
