Motorized 3-Way Valve Saunier Duval Isofast/Themafast - Ref. S1025500
The motorized 3-way valve Saunier Duval Isofast/Themafast - Ref. S1025500 allows switching water between the heating circuit and the domestic hot water circuit. When it fails, the user may notice that there is hot water but no heating, or vice versa, and there may even be a mixing of both circuits. It is installed in boilers such as F 35 E-A, F 30 E-A, C 35 E-A, F 25 E, among others. It is recommended to replace it if the fault code F.20 appears, which indicates a safety disconnection due to a temperature limiter.
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
There is heating but no hot water coming from the tap, or vice versa.
Cause: The valve is stuck in one position and does not distribute water to the other circuit.
Request each service separately (only DHW, only heating) to confirm that the fault is in the distribution and not in another component, such as the pump or the flow sensor.
- 02
The valve takes too long to switch, or the boiler shows a fault code just when switching.
Cause: The motorized actuator does not complete the travel within the time expected by the PCB, and it interprets this as a fault.
Time how long it takes to switch services; if it clearly takes several seconds longer, it points more towards the actuator than a false contact.
- 03
Buzzing or vibration in the actuator every time it requests a different service.
Cause: The motor tries to move a jammed shutter, usually due to scale buildup in the body.
Check if the buzzing stops on its own or persists for several seconds; if it persists, check for visible scale on the connections near the group before replacing it.
- 04
Water leak in the area of the valve group, dripping down.
Cause: The seals of the hydraulic body of the group have lost tightness.
Clean and dry the area, let the boiler run for a while in each mode, and confirm where the water is actually coming from before assuming it is the gas valve.
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 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 valve with a motorized actuator work for my boiler Themafast F 25 E?
Does it include the motorized actuator or do you have to buy it separately?
Does this valve also fit an Isosplit C 24 EV?
Spare parts related to Saunier Duval Isofast
