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F.28

Vaillant Boiler

Severity: Moderate

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

Vaillant Boiler F.28 — Ignition Failure

What it means

F.28 means the boiler attempted ignition but failed during startup.
The most common causes are no gas supply, a closed gas valve, a dirty ignition electrode, or condensate trap blockage.

Affected Models

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

Common Causes

  • Gas supply turned off at the meter or service valve
  • Empty bulk LPG tank
  • Dirty or worn ignition electrode
  • Blocked condensate pipe / frozen condensate in winter
  • Faulty gas valve
  • Air in the gas line (especially after work on the system)

How to Fix It

  1. Check the gas supply.

    Verify the gas service valve under the boiler is open (lever in line with the pipe).
    Test other gas appliances — if your gas hob does not work either, the issue is upstream.

  2. Check the condensate pipe (winter).

    If the condensate pipe runs outside, it can freeze.
    A frozen condensate causes the boiler to lock out.
    Pour warm (not boiling) water over the external pipe to thaw it.

  3. Reset the boiler.

    Most Vaillant boilers have a reset button on the front display.
    Press and hold for 5 seconds.
    If F.28 returns, the cause has not been resolved — call a Gas Safe engineer.

  4. Call a Gas Safe engineer for persistent F.28.

    Do not attempt internal gas component repairs.
    A registered engineer can clean or replace the ignition electrode, test the gas valve, and check pressures.

When to Call a Professional

Working on a gas boiler requires a Gas Safe registered engineer in the UK.
After basic checks (gas supply, condensate), call an engineer — do not open the boiler casing.

Frequently Asked Questions

How many times should I reset a Vaillant boiler showing F.28?

Vaillant recommends no more than 3 reset attempts. After that, the lockout indicates a fault that needs professional diagnosis. Repeated reset attempts are not safe.

Can a frozen condensate pipe cause F.28?

Yes — common in cold weather. The condensate pipe (usually a 22mm white plastic pipe leaving the boiler) freezes if it runs outside or through an unheated area. Thawing usually resolves F.28 immediately.