Verified boiler fault code
Vokèra A09 Fault Code (Vision C)
Flue thermistor or flue-thermistor counter fault, or flue thermistor overtemperature.
Safety disclaimer
Fault code summary
- Manufacturer
- Vokèra
- Fault code
- A09
- Fault type
- Flue, Temperature sensor, Overheating
- Severity
- Not specified
- Reset
- The Vision C table specifies Reset and an operation check for the overtemperature variant.
- Applicable models
- Vision Combi 25 C, Vision Combi 30 C
Quick answer
Flue thermistor or flue-thermistor counter fault, or flue thermistor overtemperature.
What does this fault code mean?
Flue thermistor or flue-thermistor counter fault, or flue thermistor overtemperature.
Common causes
- Flue thermistor fault.
- Flue thermistor counter fault.
- Flue thermistor overtemperature.
Symptoms
- Vision C displays A09 as a temporary or final alarm depending on the condition.
What can the homeowner safely check?
- Record the code and do not obstruct or dismantle the flue.
Boiler reset information
The Vision C table specifies Reset and an operation check for the overtemperature variant.
When should I call an engineer?
Contact a suitably qualified heating engineer when the fault persists, the boiler locks out, or the manufacturer instructions do not resolve it. For gas appliance work in the UK, use a Gas Safe registered engineer.
Engineer diagnosis
- Check the flue thermistor, counter, wiring and flue system.
Applicable boiler models
Related fault codes
- A01 — Vision C
Ignition failure, flame not sensed, or internal fault.
Read fault code - A02 — Vision C
Limit thermostat fault.
Read fault code - A03 — Vision C
Fan tachometer signal fault.
Read fault code - A04 — Vision C
Insufficient system water pressure.
Read fault code - A06 — Vision C
Domestic-hot-water thermistor fault.
Read fault code - A07 — Vision C
Primary-flow thermistor fault, overtemperature or temperature differential condition.
Read fault code - A08 — Vision C
Return thermistor fault, overtemperature or inverted temperature differential.
Read fault code - A77 — Vision C
Low-temperature thermostat fault.
Read fault code
Manufacturer documentation
Vision C Users Instructions, Installation & Servicing InstructionsFAULT CODES — A09: Flue thermistor or flue thermistor counter fault; flue thermistor over temperature.
Last verified
2026-09-12
Frequently asked questions
What does Vokèra A09 mean?
Flue thermistor or flue-thermistor counter fault, or flue thermistor overtemperature.
Can I reset a Vokèra A09 fault?
The Vision C table specifies Reset and an operation check for the overtemperature variant.