Error code
Vaillant Boiler Fault Code F27
Flame detection has been lost during operation The most likely cause is intermittent gas supply issue. Check first: try the standard reset once if permitted by the manufacturer.
Quick answer
F27: what does it mean and how to fix
What does it mean?
Flame detection has been lost during operation
How to fix first
Check the boiler manual for any user-level checks allowed for this code.
Why is this happening?
Intermittent gas supply issue
When should I call an engineer?
Repeated flame-loss faults should be assessed promptly by a Gas Safe registered engineer.
What does this error code mean?
Vaillant boiler fault code F27 usually means the boiler lit initially or tried to run, but then lost flame detection and shut down for safety.
In practice, F27 is commonly linked to Intermittent gas supply issue, Flame sensing fault, or Combustion or control issue.
Start with this safe check: Check the boiler manual for any user-level checks allowed for this code. If the code returns, the fault worsens, or the appliance does not behave normally, repeated flame-loss faults should be assessed promptly by a Gas Safe registered engineer.
Why is this happening?
- Intermittent gas supply issue
- Flame sensing fault
- Combustion or control issue
How to fix this safely
- Check the boiler manual for any user-level checks allowed for this code.
- Try the standard reset once if permitted by the manufacturer.
- Stop using the boiler if the fault returns repeatedly.
Reset steps
- Use only the standard user reset process if the manual allows it.
- Arrange professional diagnosis if the flame fault returns.
When to call an engineer
Repeated flame-loss faults should be assessed promptly by a Gas Safe registered engineer.
Safety warning
Do not attempt internal gas or combustion repairs. Persistent flame faults are not a DIY job.
Useful hub links
Related flame-loss fault codes
Relevant guide
Frequently asked questions
Can I keep resetting a Vaillant boiler with F27?+
No. If F27 returns after one standard user reset, stop there and arrange a qualified engineer if the manual gives no safe next step.
Is F27 something I can repair myself?+
Boiler faults should be treated cautiously. Stay within the user checks in the manual, and leave gas, combustion, and internal boiler repairs to a qualified professional.
What does F27 mean on a Vaillant boiler?+
F27 usually means flame detection has been lost during operation. If it repeats after one safe retry, treat it as a persistent fault.
How to fix F27 on a Vaillant boiler?+
Check the boiler manual for any user-level checks allowed for this code. Try the standard reset once if permitted by the manufacturer. Stop and escalate if the code returns immediately.
Why is F27 happening on my Vaillant boiler?+
The most common reasons are Intermittent gas supply issue, Flame sensing fault, Combustion or control issue. Repeated returns usually mean the underlying component or system still needs attention.