Gas Valve Mechanism Saunier Duval Isofast F35 Ref. 123 597 0
The gas valve regulates and allows the flow of gas to the burner according to the commands from the boiler's PCB. This gas valve mechanism from Saunier Duval, with reference 1235970, is essential for the operation of models such as Isofast C 24 E V1, Isofast C 28 E1, and Isofast F 35 E1, among others. When it fails, you may notice that the boiler does not ignite, experience flame lockouts, or that the gas modulation is incorrect. It is recommended to replace this part if you observe faults such as F.26, F.27, or F.28, which indicate problems with the gas valve.
VAT included
Consult via WhatsAppSaunier Duval boilers compatible with reference 05742800
Gas valve with reference 05742800. 15 confirmed compatibilities: Isofast C 24 E V1 and Isofast C 28 E1.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval Isofast C 24 E V1 | Isofast | Contrasted |
| Saunier Duval Isofast C 28 E1 | Isofast | Contrasted |
| Saunier Duval Isofast C 28 E1 NOx | Isofast | Contrasted |
| Saunier Duval Isofast C 35 E1 | Isofast | Contrasted |
| Saunier Duval Isofast F 28 E1 | Isofast | Contrasted |
| Saunier Duval Isofast F 35 E1 | Isofast | Contrasted |
| Saunier Duval Isomax C 28 E2 | Isomax | Contrasted |
| Saunier Duval Isomax F 28 E2 | Isomax | Contrasted |
| Saunier Duval Isotwin C 24 E | Isotwin | Contrasted |
| Saunier Duval Isotwin C 24 EA | Isotwin | Contrasted |
| Saunier Duval Isotwin C 24 EV | Isotwin | Contrasted |
| Saunier Duval Isotwin C 24 EV A | Isotwin | Contrasted |
| Saunier Duval Isotwin F 24 E | Isotwin | Contrasted |
| Saunier Duval Isotwin F 24 E1 | Isotwin | Contrasted |
| Saunier Duval Isotwin F 24 EA | Isotwin | 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 the part number 05742800 is the one 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 05742800. 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 05742800 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 tries to ignite but shuts off before a flame is formed.
Cause: The internal mechanism does not open the gas flow at the right moment during ignition, and the control board shuts off for safety.
Before changing the mechanism, check that the ignition electrode produces a spark and that the flame detector is clean: if the fault is there, the symptom is identical.
- 02
A fault code related to the gas valve appears, and the boiler needs to be reset to try again.
Cause: The mechanism does not respond to the opening signal sent by the PCB, so it interprets that the gas valve is not functioning and blocks.
Measure with a multimeter if there is voltage at the connector of the mechanism before replacing it: if there is no voltage, the problem may be with the PCB and not with the gas valve.
- 03
The burner does not receive gas consistently: sometimes it ignites well and other times it goes out mid-cycle.
Cause: The mechanism does not keep the gas flow open steadily, and the flow reaching the burner is irregular.
Check for any moisture or oxidation in the connector of the mechanism, as a poor connection can cause an intermittent fault very similar to an internal fault of the gas valve.
- 04
The boiler works for heating but fails when requesting domestic hot water, or vice versa.
Cause: If the mechanism fails only partially, it may respond well to one power demand and not to another.
Check if the fault occurs the same way in both operating modes before deciding that it is the gas valve: if it only happens in one, it is also worth checking the sensor or the corresponding heat exchanger.
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 of the gas mechanism (valve ref. 05742800) is not operating or is disconnected. Check coil continuity and signal from the PCB; during demand, verify with a manometer that there is no pressure variation at the valve outlet. |
| F.27 | Safety shutdown: incorrect flame detection. | Non-sealed gas solenoid valve or one that does not close properly produces an incoherent flame signal. Check the valve's tightness (leaks) and ensure the flame extinguishes upon closing; replace the valve if it does not seal. |
| F.28 | Start-up fault: ignition failed. | The gas valve does not open or is misadjusted, preventing supply to the burner. Check that it receives command/voltage and coil continuity; measure inlet/outlet pressures during the ignition attempt. |
| F.61 | Gas valve activation fault. | Short circuit to ground in the harness or valve coils, or driver fault in the PCB prevents the valve from activating. Check insulation to ground, coil resistance, and control signal from the electronics. |
| F.62 | Gas valve fault: disconnection delay. | The valve closes late or does not seal (leaks), allowing gas to pass after the stop command. Check for the closing 'click', immediate drop in ionisation, and absence of gas/flame; perform a tightness test and replace if it does not close in time. |
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 05742800
- Catalogue reference
- 05742800
- Brand
- Saunier Duval
- Type of part
- Gas valves
- Units in stock
- 5 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- 1-2 business days
- Return
- 14 days
Data read on the part and in the manufacturer's documentation
What we have not been able to verify does not appear here.
- Reference (screen printing)
- 123 597 0
- Supply voltage
- 24 VDC
- Power
- 6 VA
- Type of gas
- Natural gas (GAZ NATUREL)
Frequently asked questions about the gas valve 05742800
What reference is engraved on the gas valve mechanism of the Isofast F35?
What voltage does the gas valve mechanism of the Isofast F35 operate at?
Does this mechanism also work for the Isotwin C 24 E?
Spare parts related to Saunier Duval Isotwin
