Vaillant · Current Vaillant F-code boilers
F.57Incorrect combustion in comfort mode
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 remove the boiler case or interfere with the flue.
- If the manual identifies a frozen external condensate pipe as a possible cause, follow only the manufacturer's external thawing instructions.
- Otherwise switch the boiler off and arrange a Gas Safe registered engineer.
How an engineer may fix it
Inspect the flue and air path, condensate system, burner, fan or Venturi, sensors and combustion readings; clear, repair, adjust or replace as the appliance instructions require.
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.