Verified boiler fault code
Vokèra A77 Fault Code (Vision C)
Low-temperature thermostat fault.
Safety disclaimer
Fault code summary
- Manufacturer
- Vokèra
- Fault code
- A77
- Fault type
- Temperature sensor, Safety lockout
- Severity
- temporary
- Reset
- Not specified
- Applicable models
- Vision Combi 25 C, Vision Combi 30 C
Quick answer
Low-temperature thermostat fault.
What does this fault code mean?
Low-temperature thermostat fault.
Common causes
- Low-temperature thermostat fault.
Symptoms
- Vision C displays A77 as a temporary alarm.
What can the homeowner safely check?
- Record the code and contact the installer if it persists.
Boiler reset information
Reset information was not provided in the verified manufacturer source. Do not repeatedly reset an unresolved fault.
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
- Test the low-temperature thermostat and its circuit.
Applicable boiler models
Related fault codes
- A01 — Vision C
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Insufficient system water pressure.
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Domestic-hot-water thermistor fault.
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Primary-flow thermistor fault, overtemperature or temperature differential condition.
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Flue thermistor or flue-thermistor counter fault, or flue thermistor overtemperature.
Read fault code
Manufacturer documentation
Vision C Users Instructions, Installation & Servicing InstructionsFAULT CODES — A77: Low temperature thermostat fault; Temporary; Check low temperature thermostat.
Last verified
2026-09-12
Frequently asked questions
What does Vokèra A77 mean?
Low-temperature thermostat fault.