- Boilers
- Gas boiler
F81
Vaillant F81 on a gas boiler: cylinder charging incomplete
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On an ecoTEC exclusive system with actoSTOR, F81 together with F91 means cylinder charging has not finished in time. Record both messages and arrange a gas technician to inspect the charging circuit.
Safety first
Stop and check this first
- If you smell gas while F81 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.
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: Examine hydraulic charging
- Do not attempt this professional task: Verify sensors and pump signalling
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.
Examine hydraulic charging
What they doA qualified gas professional checks the actoSTOR pump, air, three-way valve and secondary exchanger to locate the charging restriction.
They must show youthe charging-circuit test results.
In writingthe restriction or component that prevented cylinder charging.
Verify sensors and pump signalling
What they doThe engineer checks charging and cylinder sensor responses and examines the pump harness before completing the diagnosis.
They must show youthe charging sensor and wiring checks.
In writingthe cause of F81 with F91 and the subsequent charging test.
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 F81 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 F81 and F91 alternate on the screen and whether your documents identify an actoSTOR cylinder; use only the display and documents already available.
- Meaningful result: the particular context of F81 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 F81 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 F81 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
- ecoTEC exclusive F81
- F.81
- Vaillant F81
What it means
The table specifies F81 only in combination with F91: the cylinder remains incompletely charged after the allowed period. Diagnosis covers charging and cylinder sensors, air in the actoSTOR pump, pump wiring, the paddle sensor or restrictor, three-way valve, secondary heat exchanger and pump. The pump-fault label therefore does not justify replacing the pump without checking the wider charging process.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas while F81 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
Symptoms and causes
Probable causes · in order
- Poor charging circulationPossible
The table identifies air in the actoSTOR pump, a defective pump or three-way valve, and a blocked secondary heat exchanger.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03
- Charging measurement and controlPossible
The charging and cylinder sensors, paddle sensor or restrictor, and pump wiring harness are all listed inspection points.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03
Virtual technician
Does F81 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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