- Boilers
- Gas boiler
F28
Vaillant boiler F28: no valid flame was detected during ignition
Evidence linked to this decision
View source: Vaillant UK boiler fault codesRisk level
High
Professional inspection is recommended.
Urgency
Immediate
Quick answer
F28 means no valid flame was detected during ignition in the cited model family. Do not buy a part from the display. First record whether the code occurs before any flame, or after the boiler had already been running; also note any notified gas outage without testing another appliance. F28 before flame and F29 after established operation are different branches; neither proves a gas valve.
Safety first
Stop and check this first
- Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Safe checks you can perform
- Capture the failure pattern before clearing it
- Run the safe discriminating check
- Use recurrence as the decision point
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measured service test for F28
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.
Measured service test for F28
What they doPerform gas-supply, ignition, ionisation, condensate and flue checks with combustion instruments.
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.
Capture the failure pattern before clearing it
Photograph F28, both exact model identifiers and the operating state. Record whether the code occurs before any flame, or after the boiler had already been running; also note any notified gas outage without testing another appliance.
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Run the safe discriminating check
Stay outside sealed or powered compartments. F28 before flame and F29 after established operation are different branches; neither proves a gas valve. If the observation is unclear, stop and treat the internal branch as unresolved.
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Use recurrence as the decision point
Only if the exact user manual permits it and no stop condition exists, make one controlled attempt. If F28 returns, stop; repeated resets destroy evidence and can worsen the fault.
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Virtual technician
Does F28 still appear after these checks?
This guided flow uses the exact code and your answers to choose a test, an expected result and the next branch.
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
- caldera Glow-worm F28
- erreur F28 chaudière
- Error F28 Saunier Duval
- Error F28 Vaillant
- errore F28 caldaia
- F28
- Fallo F28 Thema NOx
- Glow worm boiler F28 fault
- Glow worm F28
- Glow-worm F.28
- Glow-worm F28
- Saunier Duval boiler F28
- Saunier Duval F28
- Saunier Duval Thema NOx F28
- Vaillant F.28
- Vaillant F28
- Vaillant F28 fault
- Vaillant Fehler F28
What it means
Vaillant's official regional documentation associates F28 with no valid flame was detected during ignition. That is the controller's observed condition, not a universal failed component. Confirm the exact model before using this decision path; the same code can mean something else on another product family.
Warnings and stop conditions
- Highsource verified
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Symptoms and causes
Probable causes · in order
- First branch to separate: an interruption in the documented gas/air/condensate pathPossible
The documented condition is no valid flame was detected during ignition. Discriminating observation: Record whether the code occurs before any flame, or after the boiler had already been running; also note any notified gas outage without testing another appliance. Expected reading and decision: F28 before flame and F29 after established operation are different branches; neither proves a gas valve.
Evidence: Vaillant UK boiler fault codes list
- If that branch is ruled out: electrode, gas valve, flame signal or combustion-control faultPossible
electrode, gas valve, flame signal or combustion-control fault remains possible only after the safe observation is recorded. The next evidence is measured, not another reset: Perform gas-supply, ignition, ionisation, condensate and flue checks with combustion instruments.
Evidence: Vaillant UK boiler fault codes list
Sources and technical references
- 1
Vaillant UK boiler fault codes
Vaillant UK · official_doc
- 2
Vaillant ecoTEC installation and maintenance instructions 0020193966_04
Vaillant UK · 2020 · manual
- 3
Health and Safety Executive · official_doc
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