3-Way Valve Saunier Duval Themafast F 24 E Ref. S1020900
The 3-way valve Saunier Duval Themafast F 24 E (Ref. S1020900) is a component that regulates the flow of water between the heating circuit and the domestic hot water circuit. If it malfunctions, 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 valve is compatible with several models from the Themafast range, including the Themafast C 24 E, C 28 E, and F 30 E, among others. It is recommended to replace it when the mentioned symptoms are detected or if the fault code F14 is activated, which indicates an overheating in the heating supply.
VAT included
Consult via WhatsAppSaunier Duval boilers compatible with reference S1020900
Three-way valve with reference S1020900. Six confirmed compatibilities: Themafast C 24 E and Themafast C 24 E NOX.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval Themafast C 24 E | Themafast | Contrasted |
| Saunier Duval Themafast C 24 E NOx | Themafast | Contrasted |
| Saunier Duval Themafast C 28 E | Themafast | Contrasted |
| Saunier Duval Themafast F 24 E | Themafast | Contrasted |
| Saunier Duval Themafast F 24 E NOx | Themafast | Contrasted |
| Saunier Duval Themafast F 30 E | 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. S1020900 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 S1020900. 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 S1020900 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 radiators heat up when you only request hot water from the tap.
Cause: The three-way valve does not completely close the passage to heating and allows water to pass through both circuits simultaneously.
With the boiler cold, check if the valve shaft moves freely between the two positions or if it is stuck.
- 02
The domestic hot water takes a long time to come out hot or comes out lukewarm.
Cause: The valve does not fully switch to the domestic hot water circuit and gets stuck halfway.
Listen to see if the valve motor makes the switching click when a tap is opened; if you don't hear it, the suspicion points here.
- 03
The heating is not warming up even though the boiler ignites and modulates well.
Cause: The valve gets stuck in the domestic hot water position and does not divert water to the heating circuit.
Check for leaks or drips around the valve body, a typical sign that the internal seat is no longer sealing.
- 04
A buzzing or knocking sound is heard in the area of the valve when switching between domestic hot water and heating.
Cause: The motor forces the position change because the internal mechanism resists.
Check for any limescale or dirt blocking the stem's path before replacing the complete gas valve.
Fault codes from Saunier Duval that this spare part resolves.
| Code | Fault | Diagnosis and solution |
|---|---|---|
| F14 | Overtemperature in heating flow (>95 °C) – limiter triggered. | If the 3-way valve gets stuck in the heating position during a DHW demand, it does not switch the flow to the heat exchanger, and the supply heats up very quickly causing F14; check that the V3V actuator moves and has power, force its travel/remove the actuator to verify passage and confirm that it switches. |
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 S1020900 three-way valve.
- Catalogue reference
- S1020900
- Brand
- Saunier Duval
- Type of part
- 3-way valves
- Units in stock
- 2 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 Themafast C 24 E Manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the 3-way valve S1020900
Is this Saunier Duval 3-way valve Ref. S1020900 suitable for the Themafast F 24 E?
Is this gas valve compatible with the Themafast C 24 E?
Does this valve work for the Themafast F 30 E?
What fault codes are documented for this gas valve?
How many models are compatible with this gas valve?
What is the reference for this 3-way valve?
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