Siemens Transformer 4AJ-9900-8FB For Junkers Boiler ZW24
When you turn on the hot water tap or start the heating, the Siemens 4AJ-9900-8FB transformer generates the spark needed to ignite the burner of the Junkers ZW24 boiler. If this part fails, you will notice that the boiler attempts to start repeatedly without being able to ignite the flame, which can lead to system lockout. This transformer is compatible with other models in the Junkers range. A technician should confirm through diagnosis whether it needs to be replaced when you observe these symptoms to avoid inconveniences in the supply of hot water or heating.
- Type of part
- Transformers
- Status
- Refurbished
- Catalogue reference
- 8747201257
- Warranty
- 1 year
Junkers boilers compatible with reference 8747201257
Ignition transformer with reference 8747201257. A proven compatibility: ZW24.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Junkers ZW24 | 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.
How to check if ref. 8747201257 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 8747201257. 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 8747201257
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 tries to ignite, you can hear the gas but the spark does not trigger and it locks out after a few seconds.
Cause: The transformer does not generate the necessary voltage to produce the spark at the ignition electrode.
First, check that the electrode is not dirty, wet, or misaligned: sometimes the spark does not jump from there and not from the transformer.
- 02
A crackling sound or a small arc is heard near the transformer, different from the normal ignition noise.
Cause: The internal insulation degrades over the years and the voltage leaks outside the circuit instead of going to the electrode.
With the boiler stopped and cold, check for signs of burning or moisture around the transformer and the ignition cable.
- 03
The ignition works sometimes yes and sometimes no, without a clear pattern.
Cause: A transformer that starts to fail usually gives intermittent sparks, not a fixed fault from day one.
Check that the electrical connections of the transformer are not loose or corroded before declaring it faulty.
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.
Junkers 8747201257 ignition transformer datasheet
- Catalogue reference
- 8747201257
- Uniclima internal SKU
- TRFZW24
- 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.
- Component manufacturer
- Siemens
- Component code
- 4AJ-9900-8FB
Frequently asked questions about the ignition transformer 8747201257
Is the transformer 4AJ-9900-8FB from the Junkers ZW24 made by Siemens?
Is this Siemens transformer suitable for other Junkers boilers besides the ZW24?
