Vaillant · Current Vaillant F-code boilers
F.27Flame signal detected while burner is off
This code applies to ecoTEC plus, ecoTEC plus remastered, ecoTEC pro, ecoTEC exclusive, ecoFIT pure. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Do not keep resetting the boiler or open its case.
- Arrange a Gas Safe registered engineer.
- If you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999 from outside.
How an engineer may fix it
Isolate and test the gas valve circuit, valve tightness, ignition or flame-sensing system and control board; repair or replace components and complete required gas-safety checks.
Vaillant states that meanings can vary by appliance. Confirm the exact model manual before acting.
Manufacturer source: Vaillant UK — Boiler fault codes list. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.