- Boilers
- Gas boiler
F27
Vaillant boiler F27: a flame signal exists while the gas valve should be closed
Evidence linked to this decision
View source: Vaillant UK boiler fault codes listRisk level
High
Professional inspection is recommended.
Urgency
Immediate
Quick answer
F27 means a flame signal exists while the gas valve should be closed in the cited model family. Do not buy a part from the display. First do not reset. Record whether F27 appears while there is no heat demand and keep the appliance off. Because the signal is present when flame should be absent, there is no useful user test beyond hazard screening.
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 F27
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 F27
What they doVerify flame-ionisation current and gas-valve closure timing, then complete leak-tightness and combustion checks.
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 F27, both exact model identifiers and the operating state. Do not reset. Record whether F27 appears while there is no heat demand and keep the appliance off.
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. Because the signal is present when flame should be absent, there is no useful user test beyond hazard screening. 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
Do not reset F27. Leave the equipment off and move directly to the measured professional step.
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 F27 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
- 27
- cocina LG error F27
- code erreur F27 chaudière Vaillant
- code erreur F27 lave-linge Siemens
- codice E27 Siemens
- codice F27 Vaillant
- código E27 Siemens
- código F27 Vaillant
- E00-27
- erreur E27 Siemens
- error F27 caldera Vaillant
- error F27 lavadora Siemens
- Error F27 Saunier Duval
- errore F27 caldaia Vaillant
- errore F27 lavatrice Siemens
- F 27
- F27 Siemens
- Fehlercode F27 Vaillant
- Glow worm boiler F27
- Glow worm F27
- Glow-worm F.27
- Glow-worm F27
- Glow-worm F27 flame signal
- LG F27 cooling fan self clean
- LG F27 ventilador autolimpieza
- LG horno F27
- LG oven error F27
- LG range F27
- panne F27 Vaillant
- Saunier Duval F.27
- Siemens E27
- Siemens F27
- Siemens Fehlercode E27
- Siemens Waschmaschine Fehler F27
- Siemens washer F27
- Siemens washing machine E27
- ThemaFast Condens F.27
- Vaillant boiler F27 fault
- Vaillant F.27
- Vaillant F27
- Vaillant Fehler F27
What it means
Vaillant's official regional documentation associates F27 with a flame signal exists while the gas valve should be closed. 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: a false or unsafe flame-supervision signalPossible
The documented condition is a flame signal exists while the gas valve should be closed. Discriminating observation: Do not reset. Record whether F27 appears while there is no heat demand and keep the appliance off. Expected reading and decision: Because the signal is present when flame should be absent, there is no useful user test beyond hazard screening.
Evidence: Vaillant UK boiler fault codes list
- If that branch is ruled out: electrode, harness, gas valve or control-board faultPossible
electrode, harness, gas valve or control-board fault remains possible only after the safe observation is recorded. The next evidence is measured, not another reset: Verify flame-ionisation current and gas-valve closure timing, then complete leak-tightness and combustion checks.
Evidence: Vaillant UK boiler fault codes list
Sources and technical references
- 1
Vaillant UK boiler fault codes list
Vaillant Group · 2026 · official_doc
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