Vokèra · Vision, Compact A and Unica A-code platform
A04System water pressure too low
This code applies to Vision 25C, Vision 30C, Compact A, Unica 28i, Unica 32i. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Check the pressure gauge with the system cold.
- If it is below the range stated in the boiler manual, repressurise only by following that model's user instructions.
- Stop and book an engineer if pressure drops again, rises excessively, or there is a visible leak.
How an engineer may fix it
Check for leaks, trapped air, the pressure sensor, pump and expansion vessel; repair the underlying fault before recommissioning.
Some status codes apply only to certain variants. Confirm the exact user manual.
Manufacturer source: Vokèra — Vision Combi 25C/30C User, Installation and Servicing Manual. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.