Saunier Duval Gas Valve Isofast Condens F35E Ref. S1043900
The gas valve Saunier Duval Isofast Condens F35E, reference S1043900, regulates and allows the flow of gas to the burner according to the signal from the control board. If this valve fails, you will notice that the boiler does not ignite, there may be flame lockouts or poor modulation. It is common in Isofast Condens F35E boilers, but it is also used in models from the Isomax Condens and Isotwin Condens ranges. It should be replaced when faults such as F.26, F.27, F.56, F.61, or F.62 appear, which indicate problems with the gas valve.
VAT included
Consult via WhatsAppSaunier Duval boilers compatible with reference S1043900
Gas valve with reference S1043900. Three confirmed compatibilities: Isofast Condens F35E and Isomax Condens F35E.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval Isofast Condens F35E | Isofast Condens | Contrasted |
| Saunier Duval Isomax Condens F35E | Isomax Condens | Contrasted |
| Saunier Duval Isotwin Condens F35E | Isotwin Condens | 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. S1043900 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 S1043900. 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 gas valve S1043900 resolves.
The gas valve regulates and modulates the gas flow to the burner. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
The boiler turns on and off by itself after a few seconds, and this happens several times in a row.
Cause: The gas valve does not keep the gas flow open steadily, and the flame cuts off before the control unit validates it.
Check the ionization electrode and its position relative to the flame; a dirty or misaligned electrode causes exactly this symptom.
- 02
There is no way for the flame to ignite, even though the igniter can be heard working normally.
Cause: The gas valve is not allowing gas to pass to the burner at the time of ignition.
Check the gas installation pressure with another appliance in the house before considering the gas valve as faulty.
- 03
The flame sounds or vibrates strangely, like a buzzing noise, especially when operating at low power.
Cause: The valve does not properly adjust the minimum gas flow, and the burner operates unstably at low modulation.
Increase the demand for heating or domestic hot water to force more power and check if the noise disappears; this helps confirm a modulation problem.
- 04
The boiler has been experiencing intermittent flame faults that are resolved by resetting, but they keep reappearing.
Cause: The internal solenoid of the valve starts to fail intermittently before it stops working completely.
Note the frequency of the fault and if it coincides with any pattern (cold start, after a power outage) before replacing the part.
Fault codes from Saunier Duval that this spare part resolves.
| Code | Fault | Diagnosis and solution |
|---|---|---|
| F.26 | Fault: gas valve not functioning | The stepper motor/gas valve body (S1043900) is not operating or is disconnected, so it does not open/modulate. Check with service actuator test, continuity of the harness, and resistance of coils/stepper in the valve. |
| F.27 | Safety shutdown: incorrect flame detection | The gas solenoid valve may become non-tight and allow gas to pass with the burner off, causing a flame signal out of sequence. Check the valve's tightness (bubble test/pressure drop) and ensure the flame disappears when the control board is turned off. |
| F.56 | Fault in the regulation of the circulating flow sensor | The gas valve assembly may improperly regulate the flow (defective mechanism/cable harness), causing an air-gas discrepancy. Check diagnostic readings of the MFS, continuity of the wiring to the valve, and the valve's response to the control board. |
| F.61 | Gas valve activation error | Short circuit/ground in coils or internal defect of the gas valve prevents its activation. Check control voltage from the PCB, insulation/ohmage of coils and wiring harness; replace the valve if there is a leak or coils are shorted. |
| F.62 | Gas valve fault. Disconnection delay | The valve remains stuck or non-tight and does not close in time after the stop command. Verify that the gas flow ceases when the control is cut (downstream manometer/tightness test) and that the flame signal disappears without delay; replace if there is a leak/blockage. |
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 gas valve Saunier Duval S1043900.
- Catalogue reference
- S1043900
- Brand
- Saunier Duval
- Type of part
- Gas valves
- Units in stock
- 3 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- Delivery time shown at checkout
- Return
- 14 days
Frequently asked questions about the gas valve S1043900
Is this valve suitable for the Saunier Duval Isotwin Condens F30E?
Spare parts related to Saunier Duval Isofast Condens
