Verified boiler fault code
Vokèra A08 Fault Code (Vision C)
Return thermistor fault, overtemperature or inverted temperature differential.
Safety disclaimer
Fault code summary
- Manufacturer
- Vokèra
- Fault code
- A08
- Fault type
- Temperature sensor, Overheating, Return sensor, Circulation
- Severity
- Not specified
- Reset
- The Vision C table specifies Reset, checking the pump and checking circulation for the inverted-differential variant.
- Applicable models
- Vision Combi 25 C, Vision Combi 30 C
Quick answer
Return thermistor fault, overtemperature or inverted temperature differential.
What does this fault code mean?
Return thermistor fault, overtemperature or inverted temperature differential.
Common causes
- Return thermistor fault.
- Return thermistor overtemperature.
- Inverted temperature differential.
Symptoms
- Vision C displays A08 as a temporary or final alarm depending on the detected condition.
What can the homeowner safely check?
- Record the code and contact the installer if it persists.
Boiler reset information
The Vision C table specifies Reset, checking the pump and checking circulation for the inverted-differential 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 return thermistor, pump operation, wiring and primary circulation.
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 - A09 — Vision C
Flue thermistor or flue-thermistor counter fault, or flue thermistor overtemperature.
Read fault code - A77 — Vision C
Low-temperature thermostat fault.
Read fault code
Manufacturer documentation
Vision C Users Instructions, Installation & Servicing InstructionsFAULT CODES — A08 includes return thermistor fault, return thermistor over temperature and temperature differential inverted.
Last verified
2026-09-12
Frequently asked questions
What does Vokèra A08 mean?
Return thermistor fault, overtemperature or inverted temperature differential.
Can I reset a Vokèra A08 fault?
The Vision C table specifies Reset, checking the pump and checking circulation for the inverted-differential variant.