Gas Mechanism G20 Saunier Duval Isomax F 28 E2 Ref. 05742800
The G20 gas mechanism Saunier Duval Isomax F 28 E2 Ref. 05742800 is a gas valve that regulates and allows the flow of gas to the burner according to the commands from the PCB. When it fails, the boiler does not ignite, there may be flame lockouts, or the gas modulation is incorrect, which can generate faults such as F.26 or F.28. This mechanism is compatible with boilers from the Isofast, Isomax, and Isotwin ranges, including models like Isofast C 24 E V1 and Isomax C 28 E2, among others. It should be replaced when these symptoms are detected or during preventive maintenance.
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 gas valve does not open and the boiler does not ignite at all, although the attempt to spark can be heard.
Cause: The mechanism does not move the shutter that allows gas to pass, so even if there is a spark, there is no fuel to ignite.
Before replacing it, check that no air has entered the gas installation after a recent supply cut, because the symptom is the same as that of a blocked gas valve.
- 02
The burner ignites with a small bang or delay, as if it takes time for the gas to come out.
Cause: The mechanism opens with a delay or incompletely, and the gas reaches the burner just when the spark has already ignited, causing that small ignition jolt.
Check the cleanliness of the burner and the electrode before replacing the gas valve: dirt in that area can also delay ignition and can easily be mistaken for a valve fault.
- 03
The fault mainly appears after strong humidity in the boiler room or a small water leak nearby.
Cause: The mechanism has a limited degree of protection against water, and moisture on the internal contacts can cause it to stop responding.
Check for signs of moisture or corrosion in the connector area before replacing the gas valve: if the mechanism is wet, dry it and test before replacing it.
- 04
The boiler does not receive gas steadily and shuts off by itself during combustion.
Cause: The mechanism does not keep the gas flow open firmly, and the flow fluctuates during operation.
Check that the gas filter in the installation is not dirty or blocked, as a flow restriction upstream gives the same symptom as a faulty gas valve.
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
- 7 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- Delivery time shown at checkout
- 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
- Date code (batch)
- 034/04
- Code printed on the label
- 116 6756
Frequently asked questions about the gas valve 05742800
Is this G20 gas mechanism suitable for the Saunier Duval Isomax F 28 E2?
What is the IP protection rating of the gas valve mechanism of the Isomax F 28 E2?
What fault does this gas mechanism solve in the Isofast F 35 E1?
Does this G20 gas mechanism also work for the Glowworm XtraFast 2000?
Does this mechanism work with propane gas or only with natural gas?
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