Junkers HT II-3 PCB · 8 748 301 333 for ZWC 28/32 1MFA 23

Application for the exact variant pending confirmation. Main PCB Junkers with code 8 748 301 333 and designation HT II-3 CA GA CC. Its ignition, burner modulation, pump, and safety functions require verification for this variant.

Type of part: Junkers
Status: Refurbished
internal SKU: PLC256
Warranty: 1 year

VAT included Stock · 6 units

Compatibility

Compatible Junkers boilers

Junkers. 0 confirmed compatibilities. There are 3 other models that we are still verifying.

Models pending verification

These models are associated with this reference, but we have not finished verifying them yet, so we do not consider them compatibleIf your boiler is one of them, send us a photo of the part you are going to replace and we will verify it before you purchase.

Junkers Euromaxx ZWC 24/28	Junkers	Unconfirmed
Junkers Euromaxx ZWB 28/32	Junkers	Unconfirmed
Junkers ZWC 28/32 1MFA 23	Junkers	Unconfirmed

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 code 8 748 301 333 and the designation HT II-3 CA GA CC on your PCB: these are marked on this part.
Check the rating plate that your boiler is a Junkers ZWC 28/32 1MFA 23, the one you have registered.
Compare the complete code: the official list gives 8 748 300 533 for the ZWC28/32-1MFA 23 family (by suffix) and 8 748 300 534-C for yours.
if they match, call us at 911 17 77 77 with your boiler model and we will reserve it for you.
Any questions? Send us a photo of the label of your PCB and the rating plate of the boiler from Contact.

Diagnosis and fault codes

Symptoms that require diagnosis in the junkers

Common symptoms and faults

01
The boiler does not start, it locks out or operates erratically, with F0.
Cause: it is related to a fault of this PCB (F0, internal fault of the printed circuit). The official Junkers manual for Euromaxx (7 181 465 337, series A/K, not the MFA 23) defines F0 as an internal error of the Heatronic and requests to replace the PCB (our translation from German).
02
The boiler shuts down or locks out with fault code EA.
Cause: No flame detected: lack of gas, dirty ionization electrode, or poor ionization.
Press reset once if the boiler allows it. If it repeats, have a technician check the gas, the electrode, and its cable.
03
The display turns off intermittently or the fault code F0 appears.
Cause: Internal fault of the PCB or loose connections, sometimes due to humidity in the control board enclosure.
Have a technician check the humidity and the connections before replacing the PCB.
04
The boiler stops due to overheating and displays fault code E9.
Cause: The safety limiter has been activated: it could be air in the circuit, a blocked pump, or a blown fuse on the PCB.
Bleed the air from the system. If the fault code returns, have a technician check the pump, the fuse, and the sensor.
05
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.
06
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.
07
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.
08
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.
09
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 the flame and shuts down or locks out.	Press reset once if the boiler allows it. If it repeats, have a technician check the gas, the ionization electrode, and its cable. If all that is fine, it points to the PCB.
E9	Overheating: the safety limiter has been activated.	Check that there is no air in the system and that the flow sensor is properly connected. If the fault code returns, have a technician check the pump and the fuse on the PCB.
F0	Internal fault of the PCB or its connections.	Check the humidity and the connections of the control board box before replacing it. If the fault code persists, the PCB is the suspected part: have it checked by a technician.
FA	It continues to detect flame after closing the gas.	Have a technician check the wiring of the gas valve and the electrode. If the wiring is fine, it points to the PCB.
E2	The heating flow NTC sensor is interrupted or short-circuited.	Check the flow sensor and its cable. If the sensor and the cable are fine, have a technician check the PCB.
A7	The NTC sensor for domestic hot water is interrupted or short-circuited.	Check the domestic hot water sensor and its cable. If the sensor and the cable are fine, have a technician check the PCB.
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.
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: PLC256
Brand: Junkers
Type of part: Junkers
Units in stock: 6 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.

Inventory — Indicated reference: 8 748 300 534-C
Inventory — Application indicated in inventory: ZWC 28/32 1MFA 23 Model 2
Inventory — Mounted relay: 12 A / 250 VAC 7 A / 250 VAC
Inventory — Blue circular condenser: EPCOS
Inventory — Blue condenser: 1 μF / 400 V, partial reading "1U H 400 U7"
Inventory — Visible terminals: LS, LR, N, S
Inventory — Assembled component: HT II-3 / CA CA CC
Inventory — Indicated brand: Junkers
Identification — Marked designation: HT II-3 CA GA CC
Identification — Marked code: 8 748 301 333
Identification — Marked code: HT II-3 CA GA CC
Inventory data — Indicated reference: 8 748 300 534-C
Inventory data — Application indicated in inventory: ZWC 28/32 1MFA 23
Inventory data — Application indicated in inventory: Model 2
Inventory data — Mounted relay: 12 A / 250 VAC
Inventory data — Mounted relay: 7 A / 250 VAC
Inventory data — Blue circular condenser: EPCOS
Inventory data — Blue condenser: 1 μF / 400 V, partial reading "1U H 400 U7"
Inventory data — Visible terminals: LS, LR, N, S
Inventory data — Assembled component: HT II-3 / CA CA CC
Inventory data — Indicated brand: Junkers
Pending applications to verify: ZWC 28/32 1MFA 23; "Model 2" (compatibility text, unidentified variant) — pending confirmation.

Before purchasing

To confirm: Junkers Euromaxx ZWC 24/28 —, as a family and without suffix
To confirm: Junkers Euromaxx ZWB 28/32 —, as a family and without suffix.
Do not confuse: 8 748 300 533 — PCB (Printed circuit) that the official Junkers list (2006/07) assigns to suffixes 2800 and 3589 of the ZWC28/32-1MFA 23 family, by suffix — It differs by one digit from 8 748 300 534-C and is not the 8 748 301 333 marked here: compare the complete code.
Do not confuse: 8 748 300 506 — General column PCB from the same list, without model suffix — It is not the one assigned to the suffixes 2800 and 3589 of the ZWC28/32-1MFA 23 family.
The designation appears as "HT II-3 CA GA CC" (marked) and as "HT II-3 / CA CA CC" (mounted component). Compare it with the silkscreen on your PCB.
connect the 8 748 301 333 with a Junkers/Bosch PCB; the official list gives another code, 8 748 300 533, for the family (by suffix). Code and boiler: registered.
Pending registered applications to confirm by model, variant, or programming: Junkers ZWC 28/32 1MFA 23.

Frequently Asked Questions

Frequently asked questions: junkers

Where is the code for this Junkers PCB and which one should I compare?

On the control board itself. Our unit is marked with the code 8 748 301 333 and the designation HT II-3 CA GA CC; compare them with those on your board. It also has the reference 8 748 300 534-C. Without additional external confirmation, the two codes are linked, so always compare the entire code.

Is it compatible with my Junkers ZWC 28/32 1MFA 23?

The compatibility of this variant is pending confirmation. Registered application: this PCB for the ZWC 28/32 1MFA 23 spare parts also lists 8 748 301 333 as compatible with the Euromaxx ZWC/ZWB 28/32, without indicating the suffix 1MFA 23. If your boiler has a different suffix, compare the code of your PCB or send us a photo from Contact.

Is the 8 748 300 533 from the official Junkers list valid?

The compatibility of this variant is pending confirmation. The official list of spare parts Junkers 6720611197 (2006/07) lists 8 748 300 533 as the PCB for suffixes 2800 and 3589 of the ZWC28/32-1MFA 23 family; the connection is by suffix, as the table does not write the full name of the boiler next to the PCB. It differs from 8 748 300 534-C and 8 748 301 333 marked here, and we have not been able to verify if it is another revision or another part. Compare the code of your PCB.

What does HT II-3 CA GA CC mean and what is "FD 612"?

The compatibility of this variant is pending confirmation. HT II-3 CA GA CC is the designation marked on the plate; also note "HT II-3 / CA CA CC" for the mounted component. Without additional confirmation read, explain its letters. Third-party in flame "FD 612 Steuerung" to code 8748301333, but it is not a registered reference of the manufacturer.

What other boilers use this PCB?

The compatibility of this variant is pending confirmation. Registered: the ZWC 28/32 1MFA 23. It is also applicable for the Euromaxx ZWC 24/28 and the ZWB 28/32, without suffix; we do not consider them registered with just one.

What symptoms point to this PCB and what does F0 mean?

According to this, if this PCB fails, the boiler may not start, become blocked, or operate erratically, with F0 (internal fault of the printed circuit). The official Junkers manual for Euromaxx (A/K series, not the MFA 23) defines F0 as an internal error of the Heatronic and requests the replacement of the PCB (our translation from German). No official table read with the F0 code specifically names your model: the Euromaxx manual is from the A/K series, and a third-party copy of a Junkers fault manual mentions the ZWC 28/32-1MFA without clearly stating the code. A technician should confirm the diagnosis.

Can I install it myself?

It must be installed by a qualified technician. The official service manual for the Euromaxx from Junkers states that repairs should be carried out by an authorized installer and that the main switch must be turned off before working on the appliance. The relays on this PCB are rated at 12 A and 7 A / 250 VAC.

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Junkers HT II-3 PCB · 8 748 301 333 for ZWC 28/32 1MFA 23