- Boilers
- Gas boiler
357
Viessmann 357 on a Vitodens boiler: insufficient gas supply
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
On a Viessmann Vitodens 100-W gas boiler, fault code 357 places the burner in a fault state due to insufficient gas supply. Check that your gas shut-off valve is open or your LPG tank has fuel, reset the burner once only, and call a Gas Safe contractor if 357 returns.
Safety first
Stop and check this first
- If you smell gas, do not smoke, cause sparks or touch electrical switches: close the gas shut-off valve, open windows and doors, leave the danger area and notify your gas supplier and installer from outside the building.
- Never unlock the burner repeatedly within short intervals when code 357 appears; if a single unlock does not clear it, call your heating contractor.
Safe checks you can perform
- Check the gas shut-off valve or LPG reserve
- Perform a single burner unlock on the control panel
- Static and working gas pressure and flow switch test
- Check fan cable, 4 kΩ fuel valve coil and electrode
Leave these tasks to a qualified professional
- Do not attempt this professional task: Test static and flow gas pressures and regulator
- Do not attempt this professional task: Inspect ignition electrode insulation and reset
- Do not attempt this professional task: Check the fan unit cable and 4 kΩ fuel valve coil
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Test static and flow gas pressures and regulator
What they doThe contractor confirms the main and appliance gas valves are open, tests static and flow gas pressures, and checks the sizing of the gas line and gas flow switch.
They must show youthe gas pressure gauge readings with the burner idle and during start-up.
In writingfault code 357, the static and flow gas pressures measured, and the condition of the regulator and gas flow switch.
Inspect ignition electrode insulation and reset
What they doThe contractor inspects the ignition electrode for damaged insulation and resets the appliance once the fault has been rectified.
They must show youthe condition of the ignition electrode insulation and the boiler running after the reset.
In writingthe result of the electrode inspection and confirmation that fault 357 has cleared.
Check the fan unit cable and 4 kΩ fuel valve coil
What they doIf static pressure does not drop at burner start, the contractor checks the cable to the fan unit and measures the coil resistance at the fuel valve against the approx. 4 kΩ specification.
They must show youthe ohmmeter reading across the fuel valve coil and the fan unit cable connection.
In writingthe measured coil resistance compared with 4 kΩ and any component replaced.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Check the gas shut-off valve or LPG reserve
- Who:
- you, without using tools or loosening any pipework.
- How:
- on natural gas, check that the gas shut-off valve is open; on LPG, check the fuel reserve in your tank as advised in the Vitodens user troubleshooting guide.
- Result that matters:
- ruling out an external interruption in fuel supply before calling an engineer for code 357.
- If the valve was shut or the LPG tank was empty:
- open the valve or arrange a refill, then carry out a single burner reset.
- If the gas valve is open and gas is available:
- proceed with one burner reset or contact your heating contractor.
- Evidence to keep:
- the position of the gas valve or the LPG tank level reading when fault 357 appeared.
Evidence: Viessmann Vitodens 100-W/111-W, instrucciones de servicio para el usuario de la instalación (6135869 ES 03/2026) · Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
Perform a single burner unlock on the control panel
- Who:
- you, at the boiler display.
- How:
- after noting fault number 357, press and hold the down and up arrow buttons together for about 4 seconds until the progress bar appears on the screen.
- Result that matters:
- checking whether fault 357 was caused by a temporary supply interruption that has now cleared.
- If the home screen returns and the burner lights normally:
- monitor the boiler over the next heating demand.
- If fault 357 comes back:
- do not unlock the burner again in short intervals; call your heating contractor.
- Evidence to keep:
- a photo of fault code 357 and the outcome of your single unlock attempt.
Evidence: Viessmann Vitodens 100-W/111-W, instrucciones de servicio para el usuario de la instalación (6135869 ES 03/2026) · Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
Static and working gas pressure and flow switch test
- Who:
- authorised gas contractor.
- How:
- the engineer tests static gas pressure and gas flow pressure, checks the sizing of the on-site gas pipe and gas flow switch, and watches for rising idle pressure caused by a leaking building pressure regulator.
- Result that matters:
- verifying whether gas reaches the appliance at stable pressure without tripping the gas flow switch.
- If idle pressure rises or flow pressure drops excessively:
- the regulator, flow switch or supply pipework is rectified.
- If static pressure does not drop at burner start:
- the contractor moves on to check the fan unit cable and fuel valve coil.
- Evidence to keep:
- recorded static and working gas pressure values in mbar.
Testing gas pressures and gas line components carries a risk of gas escape and explosion: authorised gas engineers only.
Evidence: Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
Check fan cable, 4 kΩ fuel valve coil and electrode
- Who:
- authorised gas contractor.
- How:
- if static pressure does not drop, the engineer inspects the cable to the fan unit, checks that the coil resistance at the fuel valve is approx. 4 kΩ and inspects the ignition electrode for damaged insulation.
- Result that matters:
- pinpointing whether the fuel valve fails to open because of its wiring, its coil or an ignition insulation fault.
- If a faulty cable, off-spec coil or cracked electrode insulation is found:
- the affected part is replaced and the boiler is reset.
- If all electrical checks pass:
- the engineer resets the appliance and confirms reliable flame establishment.
- Evidence to keep:
- measured fuel valve coil resistance in kilohms and the condition of the ignition electrode insulation.
Opening the boiler casing and testing the fuel valve and ignition assembly is strictly for qualified gas contractors.
Evidence: Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Viessmann
- Product type
- Gas boiler
Known code variants
- error 357 caldera Viessmann
- Viessmann 357
- Viessmann boiler 357
- Viessmann error 357
- Viessmann fault 357
- Vitodens 100-W 357
- Vitodens 357
- Vitodens error 357
- Vitodens fallo 357
What it means
In the contractor service manual for the Vitodens 100-W B1HF and B1KF, fault 357 means insufficient gas supply with the burner held in a fault state. Viessmann instructs the technician to confirm that the main gas valve and gas shut-off valve are open, test static and flow gas pressures, verify the sizing of the on-site gas line and gas flow switch (noting that a leaking building pressure regulator can cause pressure to rise while idle and trip the gas flow switch on restart), inspect the fan unit cable, measure roughly 4 kΩ coil resistance at the fuel valve and check the ignition electrode for damaged insulation. Code 357 alone does not prove the gas valve has failed.
Warnings and stop conditions
- Highsource verified
If you smell gas, do not smoke, cause sparks or touch electrical switches: close the gas shut-off valve, open windows and doors, leave the danger area and notify your gas supplier and installer from outside the building.
Evidence: Viessmann Vitodens 100-W/111-W, instrucciones de servicio para el usuario de la instalación (6135869 ES 03/2026)
- Highsource verified
Never unlock the burner repeatedly within short intervals when code 357 appears; if a single unlock does not clear it, call your heating contractor.
Evidence: Viessmann Vitodens 100-W/111-W, instrucciones de servicio para el usuario de la instalación (6135869 ES 03/2026)
Symptoms and causes
Probable causes · in order
- Closed gas valve or empty LPG storage tankCommon
Both the user manual and the fault 357 service table point first to a shut gas valve on natural gas or an exhausted LPG reserve.
Evidence: Viessmann Vitodens 100-W/111-W, instrucciones de servicio para el usuario de la instalación (6135869 ES 03/2026) · Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
- Incorrect gas pressure or tripped gas flow switchCommon
Out-of-range static or flow pressure, or a leaking building pressure regulator that lets idle pressure creep up and trip the gas flow switch at restart, triggers code 357.
Evidence: Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
- Faulty fan unit cable or fuel valve coilPossible
When static gas pressure does not drop at all during start-up, Viessmann points to the cable leading to the fan unit or to a fuel valve coil whose resistance differs from approx. 4 kΩ.
Evidence: Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
- Damaged insulation on the ignition electrodeLess common
Viessmann's troubleshooting checklist for fault 357 also includes damaged insulation on the ignition electrode as a cause to rule out.
Evidence: Viessmann Vitodens 100-W B1HF, B1KF, installation and service instructions for contractors (6167586 GB 06/2026)
Virtual technician
Does 357 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
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