Gas Mechanism G20 Saunier Duval Isotwin F28 EA Ref. 05742800
The gas valve regulates and allows the flow of gas to the burner under the commands of the boiler's PCB. If it fails, you will notice that the boiler does not ignite, there may be flame lockouts, or the gas modulation is incorrect, which can generate faults such as F.26, F.27, or F.28. This G20 gas mechanism is compatible with Saunier Duval boilers from the Isofast, Isomax, and Isotwin ranges, including models like Isofast C 24 E V1, Isotwin F 24 E1, among others. It is recommended to replace it when there are ignition failures or issues with the burner operation.
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 ignites, but the flame fluctuates for no reason, or it makes a knocking sound.
Cause: The stepper motor does not properly control the opening of the gas valve, which causes poor flame modulation.
Look at the flame through the peephole for a few minutes: if it fluctuates a lot without any change in the heating demand, it could be the modulation motor.
- 02
The boiler does not ignite at any time.
Cause: If the stepper motor gets stuck in the closed position, the valve does not open and there is no gas for the burner.
Check that the motor spins freely and receives power when starting the boiler before replacing it.
- 03
The boiler repeatedly locks out with a flame failure.
Cause: A motor that does not reach the minimum opening prevents a stable flame from forming, and the control unit cuts off the gas for safety.
Check the error history on the display to see if the lock always coincides with the start, which indicates a fault in the gas valve motor.
- 04
The heating heats little or takes a long time to increase in temperature.
Cause: A faulty gas modulation limits the actual power delivered by the boiler, even though the ignition works correctly.
Compare the outlet temperature with the one displayed; if there is a significant difference, first check the hydraulic circuit and the radiators.
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
- 4 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
- 01T08
- Code printed on the label
- 4000 124 246 1
Frequently asked questions about the gas valve 05742800
What voltage does the stepper motor of the gas valve of the Isotwin F28 EA operate at?
What fault indicates that this gas valve motor needs to be replaced?
Does this mechanism work for a Saunier Duval Themaclassic?
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