Boilers and water heaters, Junkers
Junkerserror codes: complete table of boiler and water heater faults
If your Junkers has stopped working and is displaying a code, here you'll find error codes Junkers explained in one place: what each one usually indicates, which models it appears on, and what to check. For the most frequent codes, you'll also find a complete guide with step-by-step diagnostics and replacement parts.
The information is based on our experience selling spare parts for conventional, low NOx, and condensing boilers, and for miniMAXX, HydroPower-Plus, Celsius, and miniMAXX Excellence water heaters. We explain it in our own words and based on what we've learned from our daily work in the store.
The four most searched codes
- EA: This usually indicates that no flame is detected. The most common cause is a lack of gas, but if you see a flame and it still ignites, it is most likely the ionization electrode.
- E9: This usually indicates overheating. It's advisable to check the pressure, radiators, air conditioning, and water pump before checking the limiter.
- A7 / E2: Temperature probes. In many cases the problem is in the cable or the connector, not in the probe.
- C6 / C4: pressure switch and smoke evacuation. In condensation, C6 may be due to the fan.
Junkers error code table
| Code | What it usually indicates | Models | What to review |
|---|---|---|---|
| EA | No flame detected: This may be due to a lack of gas, spark, or ionization failure | All boilers and water heaters with display | View guide |
| E9 | Overheating: usually indicates that the temperature limiter has been activated | All | View guide |
| A7 | It is usually related to the hot water probe (in water heaters, the outlet probe) | Boilers and heaters | View guide |
| E2 | It is usually related to the heating flow sensor (in some heaters, the inlet sensor) | Boilers, HydroPower-Plus, miniMAXX Excellence | View guide |
| E4 | It is usually related to the cold water probe or the solar input NTC | Cerapur Acu, Eur | View guide |
| Ad | This may indicate that the accumulator probe is not being detected | Boilers with storage tank | View guide |
| A9 | This could be due to a hot water probe that is incorrectly installed or measuring incorrectly | Ceraclass Excellence, Cerapur Acu, heaters | View guide |
| C6 | This usually indicates that the pressure switch is not closing (in condensation, the fan may not work) | Boilers and heaters | View guide |
| C4 | It usually indicates that the pressure switch does not open at rest | Sealed boilers and water heaters | View guide |
| C1 / C2 | It usually indicates that the pressure switch opens during operation | Sealed boilers (C1), water heaters (C2) | View guide |
| C7 | This may indicate that the fan speed signal is not being received | EurMFA | View guide |
| F7 | It usually indicates that it detects a flame when it shouldn't (appliance turned off or before the gas is turned on) | All | View guide |
| FA | It usually indicates that it continues to detect a flame after the gas has been turned off | All | View guide |
| F0 / F1 / E0 | It could be an internal error in the electronic board or a data error | All | Soon |
| b1 / b2 / b3 | This could be due to the encoder connector or an internal data error | Boilers | Soon |
| A3 / A4 / A2 / A6 | They are usually related to smoke sensors or to the escape of smoke through the draft diverter or the chamber | Natural draft boilers and water heaters | Soon |
| AA | This may be due to an excessive temperature difference or insufficient flow rate (cal) | Eur, Ceraclass Midi | Soon |
| A8 / AC | It usually indicates that communication with the regulator or module has been interrupted | Boilers with regulation | Soon |
| DC | This may indicate that the outdoor temperature probe is not being detected | Boilers with external probe | Soon |
| d3 | This could be due to a missing thermostat jumper or an activated external controller | Boilers | Soon |
| d4 / d5 / d7 | It may be related to excessive temperature, the external drive probe, or the regulating valve | Ceraclass Excellence, Cerapur | Soon |
| E1 | It usually indicates over-temperature of the outlet water (more than 85 °C) | Heaters | View guide |
| AC | It usually indicates a water flow rate above the maximum | HydroPower-Plus, Euromaxx (turbine) | View guide |
| EC | It usually indicates an intermittent failure of ionization | miniMAXX Excellence | View guide |
| Fd | This is usually because the reset button was pressed by mistake or for too long | All | Press reset again |
| US | It may indicate an electrical voltage lower than 185 V | EurMFA | Review your diet |
| P1, P2, P3… | It is usually the initialization phase, not a fault | Eur | Wait |
With Junkers error codes, it's important to keep in mind that the same code can mean slightly different things depending on the appliance family. Therefore, in each guide, we separate the cases by model, just as we typically see them in the store.
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
On models without a display, Junkers error codes are shown by LEDs or flashing indicator lights. These are the most common equivalents.
Euronline: LED combinations
The Eurline usually 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: usually indicates overtemperature, that is, that the limiter has cut out (usually corresponds to E9).
- Red + 3rd green: usually indicates that there is a spark but no flame is detected (usually corresponds to EA).
- Red + 4th green: usually indicates that it detects a flame without a spark, i.e., a false flame signal (usually corresponds to F7).
- Red + 2nd and 5th green: This may be due to poor gas evacuation (pressure switch, fan, AGÜ probe). See pressure switch guide.
- Red + 3rd and 5th green: the primary NTC is most likely open or shorted. See probe guide.
- Red + 4th and 5th green: most likely the hot water NTC is open or shorted.
- Red + 5° green: usually indicates a slight overheating (plate heat exchanger or primary NTC).
Ceraline Acu: pilot flickers
Full explanation in the Ceraline Acu blink guide .
- 1 blink: usually indicates that it does not detect a flame (EA).
- 2 blinks: This is usually due to interrupted or shorted temperature sensors.
- 3 blinks: usually indicates that the limiter has acted on the outbound (E9).
- 4 blinks: may be related to the pressure switch (MFA version) or to the smoke outlet (MFK version).
- 5 blinks: This could be an internal fault: connections, power 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 usually normal: the key lock is active, the inspection is required, the siphon filling program activates after switching on a condensing boiler, the purge function, 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. In principle, 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 reload once or twice to rule out a one-off failure. If the code returns, there's most likely an underlying cause; looping through the reload process won't fix it.
Are Junkers error codes the same as Boschcodes?
Junkers belongs to the Bosch Group, and many boilers share electronics, so many part numbers tend to match. Even so, always double-check with the exact model.
Which codes indicate that I should call a technician now?
It is advisable to notify an authorized technician if any code related to smoke evacuation (A3, A4, C1, C6) or flame (F7, FA) is triggered, especially if it recurs. These codes are related to combustion safety.
Important notice
This article is a guide based on 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.
