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F.29

Vaillant Boiler

Severity: Moderate

Source: OnlyErrorCodes.com — Every error code. One place.

Vaillant Boiler F.29 — Flame Loss During Operation

What it means

F.29 means the burner lit but the flame was lost during operation.
Common causes are low gas pressure, a dirty flame sensor, restricted flue, or condensate trap issues.

Affected Models

  • Vaillant ecoTEC Pro
  • Vaillant ecoTEC Plus
  • Vaillant ecoFIT
  • Vaillant Turbomax
  • Vaillant ecoMAX

Common Causes

  • Low gas pressure (low LPG tank, partially closed valve)
  • Dirty ionisation/flame sensor electrode
  • Blocked or partially blocked flue
  • Frozen or blocked condensate trap
  • Faulty gas valve cycling on and off

How to Fix It

  1. Reset the boiler.

    Press and hold the reset button for 5 seconds.
    F.29 may clear after a one-time disturbance.
    If it returns, the cause needs investigation.

  2. Check the condensate pipe.

    A blocked or frozen condensate pipe causes flame loss.
    If in winter, thaw the external pipe with warm water.
    If blocked by debris year-round, an engineer can clean the trap.

  3. Check the gas supply.

    Verify the gas valve at the boiler and meter are open.
    LPG tanks below 25% can deliver inadequate pressure.
    Test other gas appliances to rule out a supply problem.

  4. Call a Gas Safe engineer.

    F.29 caused by ionisation sensor or flue issues requires professional service.
    The engineer will measure gas pressure, clean the flame sensor electrode, and inspect the flue for blockages.

When to Call a Professional

Persistent F.29 requires a Gas Safe engineer to test gas pressure, clean the flame sensor, and check the flue.
Internal boiler work is not safe for non-registered persons.

Frequently Asked Questions

What is the difference between F.28 and F.29?

F.28 means ignition never succeeded. F.29 means ignition succeeded but the flame was lost during operation. F.29 typically points to flame stability issues — sensor, gas pressure, or flue.

Why does my Vaillant boiler show F.29 only in cold weather?

Almost certainly a frozen condensate pipe. The condensate trap blockage prevents proper flame stability and triggers F.29. Insulating the external condensate pipe usually fixes recurring winter F.29.