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F.21

F.21 — Pilot Flame Failure (Ecomax Pro 828E)

Vaillant · Turbomax Plus Boilers

What does F.21 mean?

This indicates that the Ecomax Pro 828E boiler's pilot flame has gone out or failed to light, preventing the main burner from igniting.

Common Causes

  • Pilot flame failed

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check your gas supply by ensuring other gas appliances in your home are working.

  2. 2

    Ensure the condensate pipe is not frozen if it runs outside. Gently thaw with warm water if needed.

  3. 3

    Try restarting the boiler by cycling its power off and on.

  4. 4

    If the pilot light still won't stay lit, contact a qualified heating engineer to check the ignition system and gas valve.

Browse all codes in this manual (55)
Verified technical data. Last updated: April 2026

Related Faults

F.00F.00 — Flow NTC Cable Defective or Broken (Turbomax Plus)F.00, F.04, F.05, F.10, F.14, F.15F.00, F.04, F.05, F.10, F.14, F.15 — NTC Sensor Fault (Ecomax Pro 828E)F.01F.01 — Feed Temperature Sensor (NTC) Fault or Open Circuit (Turbomax Plus)
Source: Vaillant Turbomax Plus Boilers
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