Saunier Duval Isofast 3-Way Valve - Ref. S1025500
The Saunier Duval Isofast 3-way valve - Ref. S1025500 is a component that regulates the flow of water between the heating circuit and the domestic hot water circuit. If it fails, you will notice that there is hot water but no heating, or vice versa, and there may even be a mixing of both circuits. This model is compatible with boilers from the Isofast range, such as the F 35 E-A, F 30 E-A, and C 35 E-A, among others. It may also display the fault code F.20, which indicates a safety disconnection due to a temperature limiter. It is recommended to replace it when it shows faults in the switching of the circuits.
VAT included
Consult via WhatsAppSaunier Duval boilers compatible with reference S1025500
3-way valve with reference S1025500. 18 verified compatibilities: F 35 E-A and F 30 E-A.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval F 35 E-A | Isofast | Contrasted |
| Saunier Duval F 30 E-A | Isofast | Contrasted |
| Saunier Duval C 35 E-A | Isofast | Contrasted |
| Saunier Duval F 35 E H-MOD | Isofast | Contrasted |
| Saunier Duval F 30 E H-MOD | Isofast | Contrasted |
| Saunier Duval Condens F 30 E | Isofast | Contrasted |
| Saunier Duval Condens F 35 E | Isofast | Contrasted |
| Saunier Duval F 35 E | Isomax | Contrasted |
| Saunier Duval F 35 H-MOD | Isomax | Contrasted |
| Saunier Duval Condens F 35 E | Isomax | Contrasted |
| Saunier Duval F 30 H-MOD | Isotwin | Contrasted |
| Saunier Duval Condens F 30 E | Isotwin | Contrasted |
| Saunier Duval F 25 E | Themafast | Contrasted |
| Saunier Duval F 30 E | Themafast | Contrasted |
| Saunier Duval C 25 E | Themafast | Contrasted |
| Saunier Duval C 30 E | Themafast | Contrasted |
| Saunier Duval Condens F 25 | Themafast | Contrasted |
| Saunier Duval Condens F 30 | Themafast | 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. S1025500 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 S1025500. 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 S1025500 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
You turn on the hot water tap and it takes much longer than usual to get hot.
Cause: The motor does not move the mechanism or does not complete the travel to the DHW circuit.
Time the actual waiting time and compare it with another faucet in the house.
- 02
The water comes out lukewarm, neither cold nor hot, even though the boiler is on and functioning.
Cause: The valve gets stuck halfway between the two circuits and mixes the water from both.
Check that it is not a low flow issue (tap with low pressure) before looking at the gas valve.
- 03
You notice water or moisture around the motor of the valve, not just on the body.
Cause: The leak can come from the body and affect the motor, or it can come directly from the joint between the two.
Dry the area and locate the exact source of the moisture.
- 04
The boiler does not switch between heating and domestic hot water no matter how much you open or close the tap.
Cause: The valve motor does not receive or execute the circuit change command.
Listen for a brief buzzing sound from the motor when you open the tap.
Fault codes from Saunier Duval that this spare part resolves.
| Code | Fault | Diagnosis and solution |
|---|---|---|
| F.20 | Safety shutdown: temperature limiter. | If the 3-way valve (priority valve) is blocked or disconnected, the primary flow does not switch correctly and the generator overheats, triggering the F.20; to verify, force the test/diagnosis that moves the valve from the service menu and check the power supply/wiring and ensure the shaft/motor are not seized. |
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 3-way valve S1025500.
- Catalogue reference
- S1025500
- 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 F 25 E Manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the 3-way valve S1025500
Is this Saunier Duval 3-way motorized valve (Ref. S1025500) compatible with my boiler?
What symptoms indicate that the 3-way valve of an Isotwin boiler needs to be replaced?
What is the difference between the valve (SKU V3VIC28EA) and Ref. S1025500 specific to the Isofast C 35 E-A range?
What fault code is documented for this gas valve?
Is the 3-way valve suitable for boilers in the Condens range?
Spare parts related to Saunier Duval Isofast
