Saunier Duval Isomax F 35 H 3-Way Valve Motor MOD Ref. S1025500
When you open the tap or turn on the heating, the Saunier Duval Isomax F 35 H MOD 3-Way Motor Valve is responsible for directing the water between the heating circuit and the domestic hot water circuit. If this valve fails, you will notice that there is hot water but no heating, or vice versa, or even that both circuits are mixing. This model is compatible with several boilers from the Isofast, Isomax, Isotwin, and Themafast ranges, among others. A technician must confirm through diagnosis whether it needs to be replaced if you experience these issues, or if the fault code F.20 appears, which indicates a safety disconnection due to a temperature limiter.
Saunier 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
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 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 that require diagnosis in the 3-way valve S1025500
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
When you request hot water, it takes a long time to heat up or it never reaches the temperature you set.
Cause: The valve does not fully switch to the DHW circuit, and part of the water mixes with the heating return.
Check if the problem occurs only when the heating is on at the same time, indicating that the valve does not properly isolate the two circuits.
- 02
The radiators also heat up when only the domestic hot water should be functioning.
Cause: The disc or piston of the gas valve has stuck in an intermediate position and allows water to flow to the heating system when it shouldn't.
With the boiler in domestic hot water mode only, touch the radiators near the boiler to see if they are receiving heat that they shouldn't.
- 03
A noise of a straining motor or a dry click is heard every time it switches from domestic hot water to heating.
Cause: The actuator pushes against accumulated scale or against a worn internal part that prevents it from reaching its final position.
Remove the actuator from the valve without opening the water circuit, and check manually if the shaft turns smoothly or is stiff.
- 04
The boiler shows a fault warning for the 3-way valve or stops responding to the demand for domestic hot water.
Cause: The control board does not confirm that the gas valve has reached the requested position within the safety time.
Note the exact code displayed on the screen; it may correspond to a fault in the actuator wiring and not just the gas valve.
Fault codes Saunier Duval that require diagnosis
| Code | Fault | Technical checks |
|---|---|---|
| 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
- Uniclima internal SKU
- V3VIF35HMOD
- Brand
- Saunier Duval
- Type of part
- 3-way valves
- Units in stock
- 3 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 35 E H-MOD Manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the 3-way valve S1025500
Does this 3-way valve fit the Saunier Duval Isomax F35 H MOD?
What is the reference for this 3-way valve?
How many models are compatible with this 3-way valve?
What fault code is documented for this gas valve?
Is this 3-way valve suitable for boilers in the Condens range?
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