Junkers Ceraline Acu: what each number of pilot light blinks means

Your Junkers Ceraline Acu boiler has locked out and the indicator light is flashing. This boiler doesn't have a code display; the number of consecutive flashes of the indicator light tells you what the fault is. Count how many times it flashes before pausing and find that number in the table.

Here is the complete table for the Ceraline Acu (ZWSE 28-5 MFK/MFA), what to check in each case and what code it corresponds to in boilers with a screen, so you can use our detailed guides.

Junkers Ceraline Acu blinking chart

Information based on the Junkers professional troubleshooting manual for the Ceraline Acu ZWSE 28-5 MFK/MFA.

Is my Ceraline MFA or MFK?

Check it on the nameplate. The difference matters for the 4-blink code:

• MFA: Sealed boiler with a fan that expels the fumes. The four blinks refer to the pressure switch.
• MFK: Natural draft boiler with chimney. The four flashes indicate flue gas escaping through the draft diverter or combustion chamber. This is a safety warning: ventilate the room and have it checked by a qualified installer.

The breakdowns explained

1 blink: no flame detected

First, check that the gas is flowing: turn on the gas valve and, if you have a gas stove, make sure it's working. If you see the flame flicker on and then go out, the gas is reaching the stove and the problem is with the sensor: the electrode might be dirty, misaligned, or the wire might be damaged. We explain this step by step in the EA error.

2 blinks: temperature sensors

A probe is open or shorted. Before buying, check the connector and cable, as they send the same signal. The manual adds an important point: check for limescale buildup. Limescale can insulate the probe and cause it to read incorrectly. More information can be found in the NTC probe.

3 blinks: overheating

The flow restrictor has tripped. Check the pressure gauge, open the radiators, and bleed them. If the pump is seized, the water won't circulate. The restrictor is almost never the culprit. Full diagnostic information is available in the E9 error.

4 blinks: pressure switch or smoke

In the MFA model, check the flue and the pressure switch tubes before checking the pressure switch itself. We explain this in the pressure switch. In the MFK model, if the flue gases aren't venting properly through the chimney, call a professional installer.

5 blinks: internal failure

The manual instructs you to first check the electrical connections and the secure fastening of the ignition cables. A loose ignition cable can cause interference that the circuit board interprets as an internal fault. Only then should you check the printed circuit board.

Spare parts for the Junkers Ceraline Acu (ZWSE)

• Electrodes for boilers ZWSE 23/28 (87167605510)
• NTC sensor for ZWC, ZWN and ZWSE boilers (87160110730)
• Temperature sensor ZWSE 28 (87145001170)
• ZWSE 23/28 boiler pump (8716747369)
• ZWSE electronic board (8748300950)
• ZWSE 24 electronic board (87483005060)
• ZWSE 23 Expansion Vessel (87167564570)

Always check the reference number on your rating plate. All parts are available in spare parts Junkers , and the rest of the codes can be found in the error code table Junkers.

Frequently Asked Questions

How do I accurately count blinks?

The pilot blinks a series of times briefly, pauses, and repeats. Count the blinks for a whole series, ideally two or three times to be sure.

Can I reset it if it flashes 4 times on a MFK?

Once, ventilate the room. If it happens again, don't persist: the fumes aren't venting properly and it's a health risk. Call a professional installer.

Is Ceraline Acu the same as EurAcu-Hit?

These are different Junkers boilers with a hot water storage tank. The Eurhas a display and shows codes; the Ceraline Acu alerts with flashing lights.