F.27
FAULT CODE
Vaillant
Flame Simulation / Safety Lockout
High Severity
Engineer Required
The boiler has detected a flame signal when there should be none, triggering a safety lockout. This is usually caused by a faulty flame sensor or water ingress on the PCB.
Step-by-Step Fix Guide
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Step 1
Do not repeatedly reset the boiler
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Step 2 Engineer only
Call a Gas Safe engineer to inspect the ionisation electrode and PCB
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.