F.29
FAULT CODE
Vaillant
Flame Loss During Operation
Medium Severity
DIY Check Possible
The boiler successfully ignited but then lost the flame during operation. Usually caused by gas pressure fluctuations, a blocked flue, or a frozen condensate pipe.
Cold Weather Note
F.29 in cold weather almost always means a frozen condensate pipe. Thaw it with warm water and the boiler should restart.
Step-by-Step Fix Guide
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Step 1
Check for a frozen condensate pipe (most common cause in winter)
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Step 2
Thaw the condensate pipe with warm water if frozen
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Step 3
Reset the boiler once
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Step 4
If fault persists, a Gas Safe engineer should test the gas valve and flue
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.