- Boilers
- Gas boiler
F26
Vaillant F.26 on a gas boiler: gas valve not working
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Vaillant F.26 means the gas valve stepper motor is faulty or disconnected. It is a gas part: only check the gas valve is open, do not open the boiler and call an authorised professional.
Safety first
Stop and check this first
- If you smell gas: do not operate switches, sockets, doorbells or phones, no flames or smoking, open doors and windows, close the meter valve and the appliance gas valve if you can, warn neighbours without using the bell, leave the building and call the gas company from outside. That is what Vaillant asks.
- Do not try to move, disconnect or adjust the gas valve: Vaillant reserves gas settings for an authorised professional and forbids breaking seals.
Safe checks you can perform
- Smell of gas
- Gas isolation valves
- Constant or intermittent code
- Gas valve check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Gas valve motor readings
- Do not attempt this professional task: Gas tightness test after the work
- Do not attempt this professional task: CO2 check after the repair
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.
Gas valve motor readings
What they doThe technician measures the stepper motor coil continuity and the voltage reaching it with the connector fitted.
They must show youthe coil and voltage readings.
In writingthe result and any part replaced.
Gas tightness test after the work
What they doIf the valve assembly or gas pipe was touched, the technician checks gas tightness as Vaillant describes.
They must show youthe test carried out.
In writingthe tightness result.
CO2 check after the repair
What they doThe technician measures CO2 content at the flue gas test point and compares it with Vaillant's table.
They must show youthe analyser printout.
In writingthe CO2 measured and whether it was adjusted.
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.
Smell of gas
- Who:
- you.
- How:
- notice whether there is a smell of gas near the boiler or in the home.
- Result that matters:
- whether there is a smell.
- If there is a smell:
- follow Vaillant's gas warning and leave the home.
- If there is no smell:
- carry on with the checks.
- Evidence to keep:
- a note of the time.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Gas isolation valves
- Who:
- you.
- How:
- check the home's gas valve and the appliance gas valve are open, as Vaillant asks when the boiler does not start. Do not touch anything else.
- Result that matters:
- whether they were open.
- If one was closed:
- open it and note whether F.26 clears; tell the technician anyway.
- If they were open:
- gas is arriving; the fault is in the valve or its connection.
- Evidence to keep:
- a photo of the valve positions.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Constant or intermittent code
- Who:
- you.
- How:
- take a photo of the display and note whether F.26 is always there or only at times. Vaillant says to call an authorised professional when an F.xx message appears.
- Result that matters:
- whether the fault is constant or intermittent.
- If it is constant:
- call the authorised professional.
- If it comes and goes:
- tell the technician; a loose contact fits better than a broken part.
- Evidence to keep:
- photos of the code with date and time.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01 · Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Gas valve check by the technician
- Who:
- authorised gas technician.
- How:
- checks the valve's stepper motor, connector, coils, voltage, multi connector and cable harness.
- Result that matters:
- where the fault is.
- If the motor fails:
- it is replaced and combustion is adjusted.
- If the motor is fine:
- connections are repaired or the board is checked.
- Evidence to keep:
- a report of what was measured and replaced.
Only an authorised gas technician touches the gas valve; Vaillant reserves gas settings for professionals.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
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 F26 Miele
- anomalie F26 Miele
- code erreur F26 lave-linge Siemens
- code erreur F26 lave-vaisselle Miele
- codice E26 Siemens
- código E26 Siemens
- E00-26
- ecoTEC F.26
- erreur E26 Siemens
- error F26 lavadora Siemens
- error F26 lavavajillas Miele
- Error F26 Saunier Duval
- Error F26 Vaillant
- errore F26 lavastoviglie Miele
- errore F26 lavatrice Siemens
- F.26
- F26 Siemens
- Fehlercode F26 Miele
- guasto F26 Miele
- Miele dishwasher F26
- Miele F26
- Miele fault F26
- Miele Geschirrspüler Fehler F26
- Saunier Duval F.26
- Siemens E26
- Siemens F26
- Siemens Fehlercode E26
- Siemens Waschmaschine Fehler F26
- Siemens washer F26
- Siemens washing machine E26
- ThemaFast Condens F.26
- Vaillant F.26
What it means
In the ecoTEC plus table, F.26 is fault: fuel valve not working. Vaillant gives a faulty or disconnected gas valve stepper motor as the cause and says to check the motor (connector, cable, coil continuity and voltage), the multi connector and the cable harness. The gas valve meters gas to the burner; without control over it the boiler cannot run safely. The code does not separate a faulty motor from a connection fault.
Warnings and stop conditions
- Criticalsource verified
If you smell gas: do not operate switches, sockets, doorbells or phones, no flames or smoking, open doors and windows, close the meter valve and the appliance gas valve if you can, warn neighbours without using the bell, leave the building and call the gas company from outside. That is what Vaillant asks.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
- Highsource verified
Do not try to move, disconnect or adjust the gas valve: Vaillant reserves gas settings for an authorised professional and forbids breaking seals.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Symptoms and causes
Probable causes · in order
- Stepper motor faultyPossible
If the technician measures the motor coils out of range with the connector properly fitted, the valve motor is the cause.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
- Connector, multi connector or harnessPossible
If the motor is fine but gets no signal or voltage, the fault is in the connections.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
- Board not driving the motorLess common
Vaillant says to check the voltage; if the motor does not get it and the cable is fine, the fault is upstream.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
Virtual technician
Does F26 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
Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
Vaillant · 2017 · manual
- 2
Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Vaillant · 2017 · manual
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