How to Fix Vokera A02 Fault Code (Safety Thermostat) UK
Vokera A02 means safety thermostat. UK diagnosis, parts to order, reset sequence.
What A02 means
Vokera A02 indicates safety thermostat. The boiler will lock out and refuse to fire until the fault is cleared.
Do not simply reset — A02 is stored in the Vokera error log and will re-trigger within minutes if the underlying part has failed.
Diagnostic sequence
Enter service mode on the Vokera boiler and read the flow/return/DHW temperatures, fan PWM, ionisation current and pump speed.
Cross-reference against the Vokera technical manual — A02 typically points to two or three candidate parts.
- Check wiring harness continuity to the suspect sensor before condemning it.
- Isolate at the fused spur, discharge and re-inspect connectors.
- Measure resistance / voltage at the PCB plug per Vokera test procedure.
Parts to have on the van
Carry a set of NTC sensors, an ignition electrode kit and a fan for Vokera — these three parts clear >70% of A02 call-outs.
Recommission
After the fix, run the Vokera boiler through a full flow test, gas rate, and combustion analysis. Log to the Benchmark book to preserve manufacturer warranty.
Frequently asked questions
- Can I reset A02 without changing parts?
- Only if the fault has cleared (e.g. low pressure repressurised). Persistent A02 means a hardware failure.
- Which is the most common cause of Vokera A02?
- On Vokera boilers, A02 most often points to the sensor or actuator matching its meaning (safety thermostat); check wiring and connector integrity first.
- Is a Gas Safe engineer required?
- Yes — any works past the boiler case seal require a Gas Safe registered engineer under UK law.
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