Three-Way Valve Saunier Duval Themafast F25E Ref. S1025500
The 3-way valve Saunier Duval Themafast F25E Ref. S1025500 is the component responsible for switching the 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, or even that both circuits are mixing. This valve is compatible with models such as F 25 E, F 30 E, and C 25 E, among others from the Themafast, Isofast, Isomax, and Isotwin ranges. It is advisable to replace it if you observe the fault code F.20, 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
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
The hot water from the tap is working fine, but the heating won't start even though the rest is functioning.
Cause: The valve distributes water between the circuits, and if it does not switch to heating, the radiators do not receive water.
Check that the radiator valves are open and that the pump is working before considering that the valve is the problem.
- 02
The radiators lose heat suddenly when using the hot water from the kitchen or bathroom.
Cause: The internal shutter must close the heating flow while there is a demand for domestic hot water, and if it is worn out, it does not close properly.
Test by opening and closing the tap several times to see if the fault is constant or intermittent before purchasing the spare part.
- 03
A dry noise or a buzzing sound is heard in the body of the gas valve when switching modes.
Cause: The mechanism that operates the shutter can force the switch, and if it is worn out, it produces noise.
Confirm that the noise is coming from the gas valve and not from another nearby component such as the pump.
- 04
Heat is coming out of the heating circuit when it shouldn't be running.
Cause: If the shutter does not seal properly between the paths, it allows hot water to flow into the circuit that should be closed.
Check for any visible leaks on the outside of the body before assuming that the problem is with the internal sealing.
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
- 0 units
- 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 3-way valve work for a Saunier Duval Themafast F25E?
What other boilers are compatible with this 3-way valve?
Is this 3-way valve suitable for my Saunier Duval Condens F 30 E boiler?
What fault code is documented for this 3-way valve?
Can I use this 3-way valve in a boiler from the Isomax range?
Spare parts related to Saunier Duval Isofast
