F.28
Vaillant Boiler
Severity: ModerateWhat Does This Error Mean?
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
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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.
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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.
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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.
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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.