Short answer
Unlike more modern boilers, the Junkers Euroline ZW 23 does not display numerical codes on a screen, but signals faults with LED combinationsThe red indicator light (reset button) flashes with a specific pattern alongside the green temperature LEDs. In this guide, you have what each combination indicates, why it appears, and how to act, as well as the exact spare part when the fault corresponds to a component. After correcting the fault, the reset button must be pressed to turn it back on.
Euroline ZW 23 fault code table
Quick summary of all fault codes. Below you have the details of each one with its cause and solution.
| Code | Meaning |
|---|---|
| Red pilot + Green LED 45 °C | Overtemperature: the temperature limiter has activated |
| Red pilot every 1 s + Green LED 60 °C | No spark or flame signal detected |
| Red pilot every 2 s + Green LED 75 °C | Spark is detected but the flame signal is false. |
| Red pilot + Green LED 45 °C and 90 °C | Poor evacuation of combustion gases |
| Green LED 90 °C flashing | NTC sensor open or short-circuited |
What can you check yourself?
Some alerts can be resolved with simple and safe checks: replenishing the water pressure, bleeding the air from the radiators, checking that the gas valve is open, or resetting the boiler after a temporary lockout. If the code reappears after doing this, there is an underlying cause that should be reviewed by a qualified technician. Do not manipulate internal gas components nor electronics.
How to replenish the pressure step by step
- Locate the filling valve under the boiler.
- Open it slowly while observing the pressure gauge.
- Close the valve upon arrival at between 1 and 1.5 bar in cold.
- Bleed the radiators starting with the furthest one and check the pressure again.
- Reset the boiler; if the pressure warning disappears, the problem was resolved.
All fault codes and their solution
Red pilot + Green LED 45 °C — Overtemperature: the temperature limiter has been activated
Why does it appear: Temperature limiter locked, circulation pump seized, or air in the system.
What to do: Check the pressure, bleed the radiators and the boiler's air vent. If it repeats, a technician should inspect the limiter and the circulation pump.
Related spare part: Circulation pump
Red pilot every 1 s + Green LED 60 °C — No spark or flame signal detected
Why does it appear: Ignition or ionisation electrode dirty or poorly positioned, lack of gas, poor ionisation or defective gas valve.
What to do: Check that the gas valve is open and there is supply. Cleaning the electrode and inspecting the gas valve should be done by a technician.
Affected component: Gas valve
Red pilot every 2 s + Green LED 75 °C — Spark detected but flame signal is false
Why does it appear: Fault in the PCB or moisture in the printed circuit.
What to do: Requires technical inspection of the PCB and the ionisation electrode.
Related spare part: PCB (control board)
Red pilot + Green LED 45 °C and 90 °C — Poor evacuation of combustion gases
Why does it appear: Defective air pressure switch, blocked pressure switch connections, or fan not rotating properly.
What to do: Never disable the flue safety system. A technician should inspect the fan, pressure points, and air pressure switch.
Related spare part: Pressure sensor / filling key
Green LED 90 °C flashing — NTC sensor open or short-circuited
Why does it appear: NTC sensor of the primary circuit or the heat exchanger faulty or poorly connected.
What to do: Check the wiring and replace the faulty NTC sensor (technician).
Affected component: Temperature sensor
When to call a technician
Fault codes related to sensors, electronics, gas valve, fan, or flue gas evacuation require a qualified technician with the appropriate equipment. If the same fault code reappears after a reset, or if the pressure drops repeatedly, a professional inspection is advisable. In Uniclima do you find spare parts for this boiler.
Frequently Asked Questions
No. The Euroline ZW 23 does not have a numeric display: it indicates faults with combinations of the red indicator light (reset button) and the green temperature LEDs. You need to pay attention to the blinking pattern and which green LED lights up.
Pressing the reset button (the triangle with the exclamation mark) for a couple of seconds. Before turning it back on, you need to press the reset once the fault is resolved.
Identify which green temperature LED it matches with and at what rate the red one flashes: that combination indicates the type of fault (overtemperature, lack of flame, flue gas evacuation…). If you cannot resolve it with basic checks such as replenishing pressure, call a technician.