F28
FAULT CODE
Glow-worm
Ignition Failure (Modern Models)
Medium Severity
DIY Check Possible
On newer Glow-worm Energy and Ultimate models, F28 indicates the boiler has failed to detect a flame after the ignition sequence.
Cold Weather Note
F28 in winter is very commonly a frozen condensate pipe — the same fix applies across all Vaillant Group boilers.
Step-by-Step Fix Guide
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Step 1
Check gas supply
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Step 2
Check for frozen condensate pipe in cold weather
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Step 3
Reset once
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Step 4
If fault persists, contact a Gas Safe engineer
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.