Boiler shows 05, will not fire, may attempt ignition then shut down

Safety first: Allow the boiler to cool fully. Isolate electrical power before removing any covers. Water in the system may be very hot.

• Check system pressure: Ensure the pressure gauge is around 1.0–1.5 bar when cold. If low, top up via the filling loop following the Vokera manual.
• Bleed radiators: Release trapped air from radiators starting from the lowest floor upwards. Re-pressurise as needed.
• Check all valves: Make sure all isolation valves on the flow and return under the boiler are fully open.
• Reset overheat stat: Some Vokera models have a manual reset overheat thermostat behind the front panel. Only press this once the boiler is cool and with power isolated.
• Engineer checks:
  • Verify pump operation and speed settings.
  • Inspect primary heat exchanger for scale or sludge blockage.
  • Check for correct bypass operation and system design issues.

If the overheat fault recurs, a professional system flush or component replacement may be required.