- Boilers
- Gas boiler
F26
Saunier Duval F.26 on a gas boiler: gas valve not working
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Saunier Duval F.26 means fault: gas valve not working. The causes are in the gas valve motor, its connections or the electronics. Do not touch anything inside the boiler. Press reset once and wait five seconds; if it stays, call the official service centre.
Safety first
Stop and check this first
- Do not touch the gas valve or its screws. Saunier Duval forbids tampering with the Offset adjustment screw, sealed at the factory, and reserves gas adjustments for a qualified installer.
- If you smell gas: Saunier Duval says to keep away from the area, open doors and windows, light no flames and do not smoke, do not touch switches, sockets, doorbells or phones, close the meter and appliance gas valves, warn neighbours without the bell, leave the building and call the gas company from a phone outside.
Safe checks you can perform
- Code on the display and other codes
- Recent work on the boiler
- One reset with the fault key
- Gas valve and its connection checked by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Motor connection and board connector
- Do not attempt this professional task: Harness and stepper motor continuity
- Do not attempt this professional task: Combustion and gas tightness after the repair
- Do not attempt this professional task: Fault memory
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.
Motor connection and board connector
What they doWith the boiler disconnected from power, the technician checks the gas valve stepper motor connector and the board multi connector.
They must show youphotos of the connectors before and after.
In writingwhich connection was wrong or that they were fine.
Harness and stepper motor continuity
What they doMeasures with a multimeter the wiring harness between board and gas valve and the stepper motor winding.
They must show youthe measured value against the manufacturer's specification.
In writingthe value, any part replaced, its reference and why.
Combustion and gas tightness after the repair
What they doAfter working on the gas valve, measures the CO2 content with an analyser and checks that no gas escapes from the appliance.
They must show youthe measured CO2 against the manufacturer's specification and the tightness test.
In writingboth results.
Fault memory
What they doThe technician reads the last 10 codes stored in the fault memory.
They must show youthe list of codes.
In writingthe codes found before they are cleared.
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.
Code on the display and other codes
- Who:
- you.
- How:
- take a photo of the display. If several faults are present, Saunier Duval shows them alternately every two seconds: wait a few seconds and note them all.
- Result that matters:
- whether F.26 appears alone or alternates with other codes.
- If it appears alone:
- the fault is in what F.26 monitors; go on to the next check.
- If it alternates with others:
- note them all; the technician needs them for the diagnosis.
- Evidence to keep:
- photos of the display with date and time.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Recent work on the boiler
- Who:
- you.
- How:
- think back to whether anyone opened the boiler recently for a service or a repair.
- Result that matters:
- whether F.26 started right after it.
- If it started after some work:
- tell the technician; the gas and air unit is removed during a service and a connection may be left loose.
- If there was no work:
- the part or its cable may have failed on its own; the technician separates them by measuring.
- Evidence to keep:
- date and report of the last service.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00 · Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
One reset with the fault key
- Who:
- you.
- How:
- press the fault clearing (reset) key and wait five seconds, as Saunier Duval describes. Do it once only.
- Result that matters:
- whether F.26 comes back.
- If it clears and stays away:
- note the date and tell the technician at the next service.
- If it persists or returns:
- do not keep resetting; call the official service centre.
- Evidence to keep:
- a photo of the display with the code and the time.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Gas valve and its connection checked by the technician
- Who:
- official service centre technician or qualified installer.
- How:
- with the boiler disconnected from power, checks the stepper motor connection, the board multi connector and the wiring harness, and measures the motor.
- Result that matters:
- whether the fault is in a connection, the cable, the motor or the electronics.
- If it was a connection:
- it is corrected and ignition is tested.
- If the motor or electronics are faulty:
- the part is replaced and combustion is checked.
- Evidence to keep:
- a report with what was measured, replaced and the final test.
The gas valve is a gas part. Saunier Duval reserves gas adjustments and repairs for a qualified installer: do not open the casing or touch the gas valve.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
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
- Saunier Duval
- 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 ThemaFast Condens table, F.26 is fault: gas valve not working. Saunier Duval gives five causes: gas valve stepper motor not connected, circuit board multi connector badly plugged in, a break in the wiring harness, faulty stepper motor and faulty electronics. The gas valve controls gas flow to the burner; if the board cannot control it, the boiler does not run. The code does not separate a faulty motor from a connection fault.
Warnings and stop conditions
- Highsource verified
Do not touch the gas valve or its screws. Saunier Duval forbids tampering with the Offset adjustment screw, sealed at the factory, and reserves gas adjustments for a qualified installer.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00 · Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Criticalsource verified
If you smell gas: Saunier Duval says to keep away from the area, open doors and windows, light no flames and do not smoke, do not touch switches, sockets, doorbells or phones, close the meter and appliance gas valves, warn neighbours without the bell, leave the building and call the gas company from a phone outside.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Symptoms and causes
Probable causes · in order
- Stepper motor not connectedPossible
Saunier Duval lists it first. It fits if F.26 appears after a service, when the combined gas and air unit is removed.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Board multi connector badly plugged inPossible
The connection fails at the board end. The technician checks it before declaring the motor faulty.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Break in the wiring harnessPossible
A cut cable between board and gas valve gives the same code. It is separated by measuring harness continuity.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Faulty stepper motorPossible
It is only confirmed when connections and cable are fine and the motor does not give a correct value when measured.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Faulty electronicsLess common
Saunier Duval puts it at the end of the list. It is considered once everything else is ruled out.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
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
Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Saunier Duval · 2016 · manual
- 2
Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Saunier Duval · 2016 · manual
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