Johnson Starley Aquair S 25 Fault codes & diagnostics

2 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Heat Interface Unit Natural Gas 25 kW Discontinued
Download the Johnson Starley Aquair S 25 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Fault codes

All 2 documented codes

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E01

Your boiler has tried to start up but failed to light the flame, so it has shut itself down to keep things safe.

High Engineer only £120-250 Shared across the range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board

Related codes

Full explanation for E01
E03

Your boiler has detected an issue with the ventilation of exhaust gases and has safely shut itself down to prevent any unsafe operation.

Emergency Engineer only £150-300 Shared across the range

Parts commonly replaced

  • Flue gas thermostat
  • Air pressure switch
  • Fan assembly

Related codes

Full explanation for E03