Gas Mechanism G20 Saunier Duval Isofast C 35 E1 Ref. 05742800
When you turn on the heating, the G20 gas mechanism of the Saunier Duval Isofast C 35 E1 activates to regulate and allow the flow of gas to the burner. If this valve fails, you will notice that the boiler does not ignite, there may be flame lockouts, or the gas modulation is not appropriate. This mechanism is compatible with several models in the Isofast range, including the Isofast C 24 E V1 and the Isofast F 35 E1. It is advisable to replace it if you experience fault codes such as F.26, F.27, or F.28.
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 does not ignite and the display shows a gas fault, not a flame fault.
Cause: The valve mechanism does not receive or execute the opening command from the control board.
Measure continuity and voltage at the connector of the mechanism before declaring it faulty.
- 02
The boiler gets locked as soon as the ignition is attempted.
Cause: If the mechanism does not open in time, the electrode does not detect a flame and the control board locks for safety.
Check that the connector of the mechanism is properly fitted; a poor connection mimics the fault of the part.
- 03
It is difficult for the boiler to turn off completely after cutting the demand.
Cause: The mechanism does not completely close the gas flow when the control board cuts the command.
Check by listening for the click of the gas valve when stopping the heating demand.
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.
- Nominal voltage
- 24 VDC
- Power
- 6 VA
- IP protection rating
- IP 20
- Type of gas
- Natural gas
- Batch code/date
- 154/02
- Code printed on the label
- 115 575 5
Frequently asked questions about the gas valve 05742800
Does the gas mechanism Ref. 05742800 fit my Isofast C 24 E V1?
What voltage does the gas valve mechanism of the Isofast C 35 E1 operate on?
What fault indicates that the gas mechanism of the Isofast F 35 E1 needs to be replaced?
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