Auxiliary PCB Saunier Duval Isofast F 35 E Ref. 05721000
When you open the hot water tap, the Auxiliary PCB Saunier Duval Isofast F 35 E Ref. 05721000 is responsible for controlling the ignition, the modulation of the burner, the pump, and the safety features of the boiler. If this part fails, the boiler may not start, become locked, or behave erratically, which could manifest with fault codes F12, F18, or F13. It is compatible with models from the Isofast and Isomax ranges, such as the C 28 E, C 35 E, and F 28 E, among others. A technician must confirm through diagnosis whether it is necessary to replace it when these symptoms occur or in the event of evident malfunction.
Saunier Duval boilers compatible with reference 05721000
PCB with reference 05721000. 14 verified compatibilities: C 28 E and C 28 E1.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval C 28 E | Isofast | Contrasted |
| Saunier Duval C 28 E1 | Isofast | Contrasted |
| Saunier Duval C 28 E NOx | Isofast | Contrasted |
| Saunier Duval C 28 E1 NOx | Isofast | Contrasted |
| Saunier Duval C 35 E | Isofast | Contrasted |
| Saunier Duval C 35 E1 | Isofast | Contrasted |
| Saunier Duval F 28 E | Isofast | Contrasted |
| Saunier Duval F 28 E1 | Isofast | Contrasted |
| Saunier Duval F 35 E | Isofast | Contrasted |
| Saunier Duval F 35 E1 | Isofast | Contrasted |
| Saunier Duval C 28 E | Isomax | Contrasted |
| Saunier Duval C 28 E2 | Isomax | Contrasted |
| Saunier Duval F 28 E | Isomax | Contrasted |
| Saunier Duval F 28 E2 | Isomax | 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. 05721000 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 05721000. 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 on the PCB 05721000
The PCB controls the ignition, modulation, and safety features of the boiler. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
The main display works and does not show any serious errors, but the boiler does not heat as it should.
Cause: The auxiliary PCB manages part of the control of the power outputs, and if it fails, the main one does not always detect it as a clear problem.
Check if the fault occurs only with heating, only with domestic hot water, or with both; this helps to identify if it is the auxiliary or the main one.
- 02
Sometimes the boiler gets locked and needs to be reset, without an identifiable pattern.
Cause: An intermittent fault in the auxiliary PCB disrupts communication with the main one at specific moments.
Check that the connector between both PCBs is properly fitted and that the wiring does not have any exposed or burnt areas before replacing the part.
- 03
Some indicator or LED on the boiler is flashing in a way that does not match what the manual states.
Cause: The auxiliary PCB manages part of the signaling, and if it is damaged, it sends incorrect information to the main one.
Note the exact blinking pattern and compare it with the fault code table before assuming it is a fault of the auxiliary.
- 04
The boiler works but loses power or runs weak, never reaching maximum modulation.
Cause: The auxiliary PCB is involved in controlling the power delivered, and if it partially fails, it limits the modulation even if the rest of the system is functioning properly.
First, check the gas pressure and the condition of the burner; if both are correct and it still doesn't modulate, the suspicion falls on the auxiliary.
Fault codes Saunier Duval that require diagnosis
| Code | Fault | Technical checks |
|---|---|---|
| F12 | No signal from the user interface | Yes — it points to this display/interface module or its connection cable with the main PCB. |
| F18 | User interface fault | Yes — it corresponds to this display/control board module. |
| F13 | Main PCB fault | No — that code is for the MAIN PCB (a different part), not for this display. |
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.
Data sheet for the Saunier Duval 05721000 PCB.
- Catalogue reference
- 05721000
- Uniclima internal SKU
- PLCAUXISF35
- Brand
- Saunier Duval
- Type of part
- PCBs (control boards)
- Units in stock
- 5 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- Delivery time shown at checkout
- Return
- 14 days
Manuals and technical documentation
Official documentation of the boiler, useful for locating the part and cross-referencing the fault codes.
- Saunier Duval F 28 E Manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the PCB 05721000
Does this auxiliary PCB work for a Saunier Duval Isofast F 35 E?
What fault of the Isomax C 28 E requires changing this auxiliary PCB?
Is it the main PCB or the auxiliary one of the Isomax F 28 E2?
Spare parts related to Saunier Duval Isofast
