S.34
FAULT CODE
Vaillant
Frost Protection Mode Active
Low Severity
DIY Check Possible
Status code: The boiler's frost protection function has activated. The boiler will fire briefly to prevent freezing. Normal behaviour in cold weather.
Cold Weather Note
S.34 is normal and expected in cold weather. It means your boiler is working as designed to prevent pipe freeze.
Step-by-Step Fix Guide
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Step 1
No action required — this is the boiler protecting itself and the system from freezing
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Step 2
Ensure your home is adequately heated during cold periods to prevent repeat activation
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.