- Boilers
- Gas boiler
F42
Vaillant F42 on a gas boiler: gas coding resistor fault
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
F42 on an ecoTEC exclusive concerns the gas-family coding resistor or its match with D.087. Request an engineer diagnosis; do not change the gas selection through a settings menu.
Safety first
Stop and check this first
- If you smell gas while F42 is displayed, leave the building and avoid flames, smoking, switches, plugs and indoor phone use; alert others without ringing doorbells. Ventilate and close the main gas shut-off only if safe. Once outside, contact the emergency services and gas supplier emergency service, and prevent re-entry.
- With F42, fumes, a CO alarm, headache, dizziness or nausea require leaving for fresh air and seeking urgent assistance from outside. Carbon monoxide can be present without a smell; do not return to reset the boiler. Ventilate only if this does not delay escape or expose you.
Safe checks you can perform
- Assess the surroundings before reading the fault
- Gather information specific to this fault
- Technical confirmation before normal use resumes
Leave these tasks to a qualified professional
- Do not attempt this professional task: Identify the fitted coding resistor
- Do not attempt this professional task: Compare D.087 with the appliance
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.
Identify the fitted coding resistor
What they doA qualified gas professional checks the presence, condition and suitability of the resistor for the appliance gas family.
They must show youidentification of the fitted component.
In writingthe verified reference and any electrical defect.
Compare D.087 with the appliance
What they doThe engineer compares the selected gas type with the resistor and corrects discrepancies using the applicable commissioning procedure.
They must show youthe comparison of configuration and resistor.
In writingthe confirmed gas type and correction made.
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.
Assess the surroundings before reading the fault
- Who:
- you.
- How:
- before approaching the F42 display, take account of any gas smell, fumes or illness already apparent; do not search for a leak.
- Meaningful result: any sign of danger takes priority over reading the message.
- If there are warning signs:
- follow the safety advice and leave.
- If none are present:
- record the visible message without dismantling anything.
- Evidence to keep:
- when the signs appeared, once you are safely outside.
Evidence: Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Gather information specific to this fault
- Who:
- you.
- How:
- note whether F42 began after electronic repairs or a gas conversion; use only the display and documents already available.
- Meaningful result: the particular context of F42 that the service engineer will receive.
- If information is missing:
- report it as unknown rather than opening the appliance.
- If available:
- include it when requesting assistance.
- Evidence to keep:
- the complete code, model and circumstances of the warning.
Evidence: Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Technical confirmation before normal use resumes
- Who:
- a qualified gas professional.
- How:
- follow the ecoTEC exclusive diagnostic branch for F42 and examine the items listed in the professional actions.
- Meaningful result: an identified cause followed by a satisfactory verification.
- If the fault remains:
- continue diagnosis without bypassing protection.
- If corrected:
- explain the repair performed.
- Evidence to keep:
- a service record covering diagnosis and final verification.
Diagnosing F42 requires professional access to a gas appliance; you must not remove its panels or work on its connections.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03
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
- Vaillant
- Product type
- Gas boiler
Known code variants
- anomalía F42 Miele
- anomalie F42 Miele
- code erreur F42 lave-vaisselle Miele
- ecoTEC exclusive F42
- error F42 lavavajillas Miele
- errore F42 lavastoviglie Miele
- F.42
- Fehlercode F42 Miele
- guasto F42 Miele
- Miele dishwasher F42
- Miele F42
- Miele fault F42
- Miele Geschirrspüler Fehler F42
- Vaillant F42
What it means
For this ecoTEC exclusive generation, F42 identifies gas-family coding on the circuit board. The manufacturer lists a missing resistor, an open or short circuit, and a mismatch between the fitted resistor and the gas type selected in D.087. Diagnosis therefore covers both the physical component and configuration, particularly following electronic work. The code alone does not establish a gas supply interruption.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas while F42 is displayed, leave the building and avoid flames, smoking, switches, plugs and indoor phone use; alert others without ringing doorbells. Ventilate and close the main gas shut-off only if safe. Once outside, contact the emergency services and gas supplier emergency service, and prevent re-entry.
Evidence: Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
- Criticaleditorial warning
With F42, fumes, a CO alarm, headache, dizziness or nausea require leaving for fresh air and seeking urgent assistance from outside. Carbon monoxide can be present without a smell; do not return to reset the boiler. Ventilate only if this does not delay escape or expose you.
Evidence: Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Symptoms and causes
Probable causes · in order
- Missing resistor or broken circuitPossible
The board gas coding resistor can be absent, have an open circuit or present a short circuit.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03
- Incompatible gas selectionPossible
The fitted resistor may disagree with the gas type selected in D.087; either selection can be incorrect according to the fault table.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03
Virtual technician
Does F42 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
- 1
- 2
Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Vaillant · 2016 · manual
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