Vokèra · Vision, Compact A and Unica A-code platform
A09Flue thermistor or service-counter fault
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
- Do not remove the boiler case or interfere with the flue.
- If the manual identifies a frozen external condensate pipe as a possible cause, follow only the manufacturer's external thawing instructions.
- Otherwise switch the boiler off and arrange a Gas Safe registered engineer.
How an engineer may fix it
Inspect the flue and air path, condensate system, burner, fan or Venturi, sensors and combustion readings; clear, repair, adjust or replace as the appliance instructions require.
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.