Viessmann · Selected Vitodens and Vitotronic ranges
A4Air lock in internal circulation pump or minimum flow not achieved on Vitodens 222-F
This code applies to Vitodens 100-W, Vitodens 200-W, Vitodens 222-F, Vitotronic 100, Vitotronic 200, Vitotronic 200-H, Vitotronic 300, Vitotronic 300-K, Vitocontrol-S. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Check the system pressure and make sure accessible radiator valves are open.
- Allow an overheated boiler to cool and reset once only if the user manual permits it.
- If the fault returns, stop resetting and arrange an engineer.
How an engineer may fix it
Diagnose water circulation, air locks, pump operation, valves, bypass, blockages, heat exchanger and temperature sensors; restore correct flow and test the safety controls.
Viessmann warns that the same code can have different meanings on different models. The exact manual must take precedence.
Manufacturer source: Viessmann UK — Fault Code Checker. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.