3-Way Valve Saunier Duval Isofast Condens F35 E Ref. S10255
If you notice that you have hot water but no heating, or that both circuits are mixing, it is likely that the Saunier Duval Isofast Condens F35 E Ref. S10255 three-way valve is failing. This valve is responsible for directing water between the heating circuit and the domestic hot water circuit. The most common faults associated are F.318, which indicates that the valve is not moving, and F.326, which points to a malfunction of several hydraulic components. It is compatible with models such as Isofast Condens F 35 E, Isofast Condens F 30 E, and others from the Isofast range, among others. You should replace it when you observe the mentioned symptoms or if it shows evident malfunction.
VAT included
Consult via WhatsAppSaunier Duval boilers compatible with reference S10255
3-way valve with reference S10255. 28 verified compatibilities: Isofast Condens F 35 E and Isofast Condens F 30 E.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval Isofast Condens F 35 E | Isofast | Contrasted |
| Saunier Duval Isofast Condens F 30 E | Isofast | Contrasted |
| Saunier Duval Isofast Condens F 35-A | Isofast | Contrasted |
| Saunier Duval Isofast 21 Condens F 25 | Isofast | Contrasted |
| Saunier Duval Isofast 21 Condens F 35-B | Isofast | Contrasted |
| Saunier Duval Isofast 21 Condens F 30-B | Isofast | Contrasted |
| Saunier Duval Isofast F 30 E H-MOD | Isofast | Contrasted |
| Saunier Duval Isofast F 35 E H-MOD | Isofast | Contrasted |
| Saunier Duval Isomax C 30 | Isomax | Contrasted |
| Saunier Duval Isomax Condens F 35 E | Isomax | Contrasted |
| Saunier Duval Isomax Condens F 35-B | Isomax | Contrasted |
| Saunier Duval Isomax F 35 H-MOD | Isomax | Contrasted |
| Saunier Duval Isotwin C 30 | Isotwin | Contrasted |
| Saunier Duval Isotwin Condens F 30-A | Isotwin | Contrasted |
| Saunier Duval Isotwin F 30 H-MOD | Isotwin | Contrasted |
| Saunier Duval Themafast C 25 E | Themafast | Contrasted |
| Saunier Duval Themafast C 30 E | Themafast | Contrasted |
| Saunier Duval Themafast F 25 E | Themafast | Contrasted |
| Saunier Duval Themafast F 30 E (2004) | Themafast | Contrasted |
| Saunier Duval Themafast F 25 E H-MOD | Themafast | Contrasted |
| Saunier Duval Themafast F 30 E H-MOD | Themafast | Contrasted |
| Saunier Duval Themafast NOx F 25-A LPG/GN | Themafast | Contrasted |
| Saunier Duval Themafast NOx F 30-NL/LL | Themafast | Contrasted |
| Saunier Duval Themafast Condens F 24 E | Themafast Condens | Contrasted |
| Saunier Duval Themafast Condens F 25 | Themafast Condens | Contrasted |
| Saunier Duval Themafast Condens F 30 E | Themafast Condens | Contrasted |
| Saunier Duval Themafast Condens F 30 (2010) | Themafast Condens | Contrasted |
| Saunier Duval Themafast Condens F 30 H-MOD | Themafast Condens | 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. S10255 is the part for your boiler
What determines it is not the boiler model, but the reference printed on the part you already have installed.
- Find the reference printed on the installed part and check whether it matches the catalogue reference S10255. 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 and faults that the S10255 three-way valve resolves.
The 3-way valve diverts water between heating and domestic hot water. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
The hot water tap is coming out cold or takes a long time to heat up, even though the heating is working fine.
Cause: The valve did not switch and does not open the flow to the domestic hot water circuit.
Turn the tap on and off a couple of times in quick succession and see if it heats up during any attempt; if it’s intermittent, it points more towards a switching fault.
- 02
With domestic hot water available, the heating does not start or the radiators remain lukewarm.
Cause: The valve prioritizes the DHW circuit and does not allow flow to heating when it should.
Confirm that the thermostat or the control is requesting heating before suspecting the gas valve.
- 03
There is a knocking or vibration in the pipe when it switches service.
Cause: The internal mechanism does not move smoothly and jerks when reaching the final position.
Note the exact moment in the cycle when the noise occurs; if it always happens when switching modes, it matches the typical pattern of this part.
- 04
There is moisture or dripping around the body of the gas valve, not on the surrounding pipes.
Cause: The wear of the internal seals allows water to leak out of the body.
Clean and dry the area, and check again after a complete cycle to confirm that the source is the gas valve and not a loose connection.
Fault codes from Saunier Duval that this spare part resolves.
| Code | Fault | Diagnosis and solution |
|---|---|---|
| F.318 | The 3-way motorised valve is not moving. | The 3V motor/actuator is blocked or without power, so it does not switch between heating and DHW. Check by powering and operating the 3V with the tests (e.g., P.008/T.002) and checking its position in diagnosis (e.g., D.035/D.070), motor continuity, and ensure it is not mechanically stuck. |
| F.326 | The hydraulic test detects that at least two hydraulic components are not functioning. | A blocked 3V or a loose connector causes the hydraulic self-check to fail. Confirm by ordering the movement of the 3V (tests P.008/T.002), checking its position in diagnosis (D.035/D.070), and verifying wiring, motor continuity, and free movement of the shaft. |
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 S10255 three-way valve.
- Catalogue reference
- S10255
- Brand
- Saunier Duval
- Type of part
- 3-way valves
- Units in stock
- 1 unit
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- 1-2 business days
- 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 Isomax Condens F 35 E Manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the 3-way valve S10255
Is this 3-way valve suitable for a Saunier Duval Isofast Condens F35 E?
Is it the same reference as the valve S1025500 from another sheet?
Does this valve work for an Isotwin Condens F30-A?
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