Refurbished Junkers Junkers

Junkers PCB 8748300455 · Euromaxx ZWC 24-1 MF2K 31

PCB located in the control panel of the boiler. This unit features a two-digit display and four buttons.

Type of part: Junkers
Status: Refurbished
internal SKU: PLC245
Warranty: 1 year

VAT included Stock · 4 units

Compatibility

Compatible Junkers boilers

Junkers. A proven compatibility: Junkers Euromaxx ZWC 24-1 MF2K 31.

Proven compatibility

Boiler model	Family	Verification
Junkers Euromaxx ZWC 24-1 MF2K 31	Junkers	Contrasted

Can't see your model or have questions? The printed reference takes precedence. How to check it · Send us a photo via WhatsApp.

Guide

How to check if it is the part for your boiler

The part reference, model, and equipment revision must be verified against the manufacturer's documentation.

Look for the printed code 8 748 300 and the handwritten suffix 455; together they form 8748300455.
Check the integrated circuit NEC JAPAN D8749H (marked 129.BE14.18, 8 744 501 318 and 0347PY011) and the relay M100965660 T904.
Compare the suffix with that of your PCB: the official breakdown of the series lists 8 748 300 454 and 8 748 300 506, which are different codes. Do not consider them as the same.
Check the rating plate that your boiler is a Euromaxx ZWC 24-1 MF2K 31.
If they match, call us at 911 17 77 77 with your boiler model and we will reserve it for you.

Diagnosis and fault codes

Symptoms that require diagnosis in the junkers

Common symptoms and faults

01
The boiler does not ignite and the screen shows EA.
Cause: No flame detected on ignition: there is no ionization current.
Check that the gas valve is open and that there is pressure. If the gas is flowing properly, have a technician check the electrode, its cable, and the PCB.
02
The screen shows F0.
Cause: Internal fault of the PCB or its circuit.
Check the contacts, plugs, and ignition and bus cables. If the fault code persists, have a technician replace the PCB.
03
The boiler does not receive the commands from the regulator properly and A8 or AC appears.
Cause: Communication interrupted between the bus module, the control unit, and the electronics.
Check the cable between the module and the control board. If the cable is fine, have a technician check the module or the PCB.
04
The boiler stops heating and the screen shows E9.
Cause: The safety limiter (STB) has been activated due to excessive temperature.
Check that the pump is circulating, bleed the system, and check the fuse on the PCB. If the fault code returns, have a technician check it.
05
On the screen, CC or E2 appears: the PCB is not reading a sensor correctly.
Cause: External sensor or interrupted flow sensor or short-circuited.
Check the affected sensor and its cable. If the sensor and the cable are fine, have a technician check it.

Junkers fault codes that require diagnosis

Code	Fault	Technical checks
EA	There is no ionization current: the boiler does not detect flame when starting.	Before checking the PCB, ensure that the gas valve is open, that there is pressure, and that the ionization electrode and its cable are in good condition. If everything is fine and the fault code persists, the PCB is likely the culprit: have a technician check it.
E9	The safety limiter (STB) has been activated due to excessive temperature.	Check that the pump is circulating, bleed the system, and check the fuse on the PCB. If the fuse is fine and the fault code returns, have a technician check it.
FA	The ionization current remains present after normal disconnection.	Check the wiring of the gas body, the gas valves, and if there is moisture in the electronics. If none of that is faulty, the PCB is the suspect: have a technician check it.
F0	Internal fault of the PCB or its circuit.	Check the connection of the electrical contacts, the plugs, and the ignition and bus cables. If the fault code persists, the PCB is suspect: have a technician replace it.
A8	Communication interrupted between the bus module and the control unit.	Check the cable between the bus module and the control unit or the regulator. If the cable is fine, the module or the PCB may be faulty: have a technician check it.
AC	Electrical interruption between the plug module and the Heatronic electronics.	Check the cable between the module and the PCB. If the cable is fine, the fault points to the control board: have a technician check it.
CC	The PCB does not detect the outdoor temperature sensor.	Check the outdoor sensor and its cable. It only appears when there is an outdoor sensor or bus regulator installed.
d3	Bornes 8-9 open: the bridge or the thermostat connector is missing.	Check the terminal strip 8-9 and the jumper before suspecting the PCB.
E2	The supply temperature sensor (NTC) is interrupted or short-circuited.	Check the flow sensor and its cable. If the sensor and the cable are fine, the PCB is reading incorrectly: have a technician check it.
AA	Excessive temperature difference between the heating supply and the domestic hot water.	Check the heating and domestic hot water sensors and if there is scale in the heat exchanger. If the sensors are fine, have a technician check it.
b1	Encoder connector on the PCB poorly mounted or defective.	Check that the encoder connector is properly mounted and measure it. If it is fine and the fault code persists, the PCB is the suspect.

These symptoms can have more than one cause. If your boiler displays a fault code, send it to us via WhatsApp along with a photo of the labeling, and we'll tell you if this is the part.

Technical data

Technical sheet: Junkers

Uniclima internal SKU: PLC245
Brand: Junkers
Type of part: Junkers
Units in stock: 4 units
Status: Refurbished
Warranty: 1 year
Shipping: Delivery time shown at checkout
Return: 14 days

Part data and available documentation

Contrast the label codes, PCB, and revision with the installed part; they are not necessarily equivalent references.

Terminal block: Terminals 1, 2, 4, 7, 8, and 9
Integrated circuit: NEC JAPAN D8749H
Integrated circuit markings: 129.BE14.18; 8 744 501 318; 0347PY011
Relay label: HT II-3; BB BA BH
Relay markings: M100965660 T904; 10 M 400 03
Visible interface: Two-digit display and four buttons
Blue component marking: 1u M 400 03
Printed PCB silkscreen: 8 748 300
Handwritten suffix on PCB: 455
Handwritten/overprinted marking in box FD: 484
Stock code: 8748300455
Identification — Printed PCB silkscreen: 8 748 300
Identification — Handwritten suffix on PCB: 455
Identification — Marked in box FD: 484
Identification — Code on bag: 8748300455
Bornera: Terminals 1, 2, 4, 7, 8, and 9
Technical sheet: Integrated circuit: NEC JAPAN D8749H
Technical sheet: Integrated circuit markings: 129.BE14.18; 8 744 501 318; 0347PY011
Relay label: HT II-3; BB BA BH
Technical sheet: Relay markings: M100965660 T904; 10 M 400 03
Visible interface: Two-digit display and four buttons
Technical sheet: Marking of the blue component: 1u M 400 03
Inventory data — Application indicated in inventory: ZWC 24-1 MF2K 31
Additional markings: Terminals 1, 2, 4, 7, 8, 9. CI NEC Japan D8749H; 129.BE14.18; 8 744 501 318; 0347PY011. Relay HT II-3; BB BA BH; M100965660 T904; 10 M 400 03. Two-digit display and four buttons. Blue component: 1u M 400 03. PCB silkscreen 8 748 300 with handwritten suffix 455; handwritten/overprinted marking FD484. Code on bag: 8748300455.
Pending applications to verify: ZWC 24-1 MF2K 31 — compatibility noted; pending confirmation by variant.

Before purchasing

Do not confuse: 8 748 300 454 — Printed circuit (PCB, pos. 4 of the control panel) in the official spare parts list 6720611196, rev. 02.10: ZC24/28-1MFK, ZSC28-1MFK and ZWC24/28-1MF2K — Same prefix, but suffix 454 and not 455. Not confirmed: whether they are equivalent.
Do not confuse: 8 748 300 506 — PCB (control board, pos. 4 of the control panel) in rev. 05.08 of the same list: ZC24/28-1MFK, ZSC24/28-1MFK and ZWC24/28-1MF2K — Suffix 506 and not 455. Rev. 02.10 gives 454 and rev. 05.08 gives 506; neither of them has 455.
Do not confuse: 8748300454 / 8748300506 — PCB module offered for the Euromax ZWC 24-1 MF2K — These are different codes and do not declare equivalence with the 455. The 506 is also listed in the official list of the MFA/MF2A family (other boilers).
The suffix 455 is handwritten: compare it with the one on your PCB. The official parts list shows in that position the 8 748 300 454 (rev. 02.10) and the 8 748 300 506 (rev. 05.08): other suffixes.
State and level measure; compatibility is confirmed. Not confirmed: 8748300455: the official breakdown gives 454 (rev. 02.10) and 506 (rev. 05.08) and 454/506 for the ZWC 24-1 MF2K. Data noted, without lowering what is confirmed.

Frequently Asked Questions

Frequently asked questions: junkers

Where is the code for this PCB and how is it read?

There are two parts: the printed silkscreen 8 748 300 and the handwritten suffix 455, which together give 8748300455 (also 8 748 300 455 or 8748300/455). The FD box has the marking 484. The integrated circuit is a NEC JAPAN D8749H with the markings 129.BE14.18, 8 744 501 318, and 0347PY011.

Is it compatible with my Junkers Euromaxx ZWC 24-1 MF2K 31?

Yes. Confirmation registered: this PCB for the ZWC 24-1 MF2K 31. Without additional external confirmation, it cites 8748300455: the official breakdown indicates in that position 8 748 300 454 (rev. 02.10) or 8 748 300 506 (rev. 05.08) and provides 8748300454 or 8748300506 for the ZWC 24-1 MF2K. They are different suffixes; for this boiler, please send the confirmation.

What is the difference between 8748300455 and 8 748 300 454 and 506 from the official parts list?

The official parts list (doc. 6720611196) indicates that the control board, pos. 4, is 8 748 300 454 in its rev. 02.10 and 8 748 300 506 in the 05.08, for the ZWC24/28-1MF2K and the ZC/ZSC-1MFK. Ours shares the prefix 8 748 300 but ends in 455, which does not appear in either of the two. Not confirmed: that they are equivalent, so it is not assumed: compare the handwritten suffix of your board.

What do 8 748 300, 455, 484, and D8749H mean?

8 748 300 is the silkscreen printed on the circuit and 455 is the handwritten suffix that completes the code. D8749H is the NEC JAPAN integrated circuit. The 484 is marked in the FD box: we have not found an explanation of what it indicates, so we do not use it to identify the PCB.

Is there anything else that needs to be checked when replacing the PCB of an Euromaxx?

The official list of the series includes the coding connector (Code plug, pos. 5) as a separate part, with a different code depending on the type of boiler and gas: 8 714 411 143, 146, 148, 151, 153, 154, 155, or 156. Before changing the PCB, check which one your boiler uses.

Does it also work for the ZWC 28-1 MF2K or for other Euromaxx models from the same list?

We cannot guarantee it. The official parts list 6720611196 covers ZC24/28-1MFK, ZSC-1MFK, and ZWC24/28-1MF2K, but in that position it shows PCBs 454 and 506; PCB 455 does not appear in either of the two revisions. This PCB has only been confirmed with the ZWC 24-1 MF2K 31. Please send us a photo of your PCB label and the boiler's specification plate from the Contact section, or call us at 911 17 77 77.

Who should install this PCB?

A qualified installer. The official spare parts list for the series indicates that the spare parts can only be installed by an authorized installer, and the PCB is located in the control panel of a gas boiler with electrical supply.

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Junkers PCB 8748300455 · Euromaxx ZWC 24-1 MF2K 31