A4
FAULT CODE
Viessmann
Air Lock in Pump / Insufficient Flow (Vitodens 222-F)
Medium Severity
DIY Check Possible
On Vitodens 222-F boilers, code A4 indicates an air lock in the internal circulation pump or insufficient minimum flow rate. The venting program starts automatically.
Step-by-Step Fix Guide
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Step 1
Allow the boiler's automatic venting program to run (may take several minutes)
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Step 2
Check system pressure
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Step 3
Bleed radiators
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Step 4
If fault persists after venting, call 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.