Siemens Junkers Transformer ZW 20 KD 23 Ref. 8747201254
The ZW range boilers from Siemens use the Siemens Junkers ZW 20 KD 23 Ref. 8747201254 transformer. This part is an ignition transformer that generates the spark needed to ignite the burner. If it fails, you will notice that the boiler attempts to start but cannot ignite the flame, which may cause a lockout. This transformer is compatible with models such as the ZW 20 KD, among others. A technician must confirm through diagnosis whether it needs to be replaced when the boiler has ignition issues.
- Type of part
- Transformers
- Status
- Refurbished
- Catalogue reference
- 8747201254
- Warranty
- 1 year
Junkers boilers compatible with reference 8747201254
Ignition transformer with reference 8747201254. A proven compatibility: 20 KD.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Junkers 20 KD | ZW | Contrasted |
Can't see your model or have questions? The printed reference takes precedence. How to check it · Send us a photo via WhatsApp.
How to check if ref. 8747201254 is the part for your boiler
The part reference, model, and equipment revision must be verified against the manufacturer's documentation.
- Find the reference printed on the installed part and check whether it matches the catalogue reference 8747201254. If it is not visible, do not identify the part from its shape alone.
- Check the full boiler model on its data plate and look for it in the model associations on this page.
- Compare the connections and physical body with the original part before installation.
- If anything is unclear, send us a photo of the marking via WhatsApp before placing your order.
Symptoms that require diagnosis in the ignition transformer 8747201254
The ignition transformer generates the high voltage for the spark of the electrodes. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
The boiler is completely dead: no display, no indicators, and no sound when turning it on.
Cause: This transformer supplies the PCB with the reduced voltage it needs; if it doesn't output, the PCB is left without power.
Check with a multimeter that mains voltage is reaching the transformer input before considering it faulty.
- 02
The display or the panel lights do not turn on even though there is power in the house.
Cause: Without the reduced voltage provided by this transformer, the control electronics have no power supply.
Check the fuses on the PCB and the boiler itself; a blown fuse can cause the same symptom without the transformer being faulty.
- 03
The boiler does not respond to anything: neither the thermostat, nor the boiler control, nor the buttons on the panel.
Cause: If the low voltage secondary does not reach the PCB, no control circuit can operate and there is no response to any command.
Before replacing the transformer, check that the connectors to the PCB are not loose, rusted, or have any frayed wires.
- 04
There is noticeable heating or a louder than usual humming in the transformer area, without the boiler starting.
Cause: A winding on the verge of failure may heat up or buzz more before completely losing voltage.
With the boiler turned off, carefully touch the transformer casing after it has been in use for a while; excessive heat or a loud buzzing sound are signs that it is malfunctioning.
- 05
The boiler stopped responding right after a power outage or a power surge in the house.
Cause: Transformers are sensitive to voltage spikes, which can damage the primary or secondary winding.
If the fault coincides with a storm or a recent power outage, it is another indication that the transformer may have been damaged.
Junkers fault codes that require diagnosis
| Code | Fault | Technical checks |
|---|---|---|
| 7U/2052 | Maximum ignition transformer activation time exceeded. | The ignition transformer remains powered for spark retries until the allowed time is exceeded; if the transformer itself is faulty (weak or absent spark) or thermally saturated, the unit locks with this code. Verify by activating the 'Zündung' test in the service menu and checking HV output/transformer condition; replace if there is no spark or it is out of range. |
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.
Ignition transformer datasheet Junkers 8747201254
- Catalogue reference
- 8747201254
- Uniclima internal SKU
- TCBZW20KD
- Brand
- Junkers
- Type of part
- Transformers
- Units in stock
- 7 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.
- Primary (Pin 5-7)
- 230 V, 50...60 Hz
- Secondary (Pin 10-12)
- 25 V, 20 VA
- Ambient temperature (ta)
- 50°C/B
- Bosch/Junkers code on label
- 8747201254
- Manufacturer and model
- Siemens 4AJ4600-8FB (according to the label, in another photo of the same part)
Frequently asked questions about the ignition transformer 8747201254
Is this transformer suitable for my Junkers ZW 20 KD boiler?
Who manufactures the transformer Ref. 8747201254 for the Junkers ZW 20 KD?
What is the output voltage of the transformer in the ZW 20 KD?
What ambient temperature can the transformer of the Junkers ZW 20 KD withstand?
Does the code 8747201254 match the one engraved on the transformer of the ZW 20 KD?
