F4
FAULT CODE
Saunier Duval
Flame Lost During Operation
Medium Severity
DIY Check Possible
The boiler ignited but then lost the flame during operation. On some Saunier Duval models, F4 is also used for a second type of ignition fault.
Cold Weather Note
F4 in winter — check condensate pipe first.
Step-by-Step Fix Guide
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Step 1
Check condensate pipe for freezing in cold weather
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Step 2
Reset once
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Step 3
If fault persists, call a Gas Safe engineer to check gas pressure and gas valve
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.