Johnson Starley Quantec 24S Fault codes & diagnostics

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

GC Number 41-416-16
Download the Johnson Starley Quantec 24S manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Fault codes

All 3 documented codes

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E03

Your boiler has temporarily shut itself down because it got too hot, and it needs a manual reset to start working again.

High Engineer only £90-200

Parts commonly replaced

  • High limit thermostat
  • Pump
  • PCB
  • NTC thermistor

Related codes

Full explanation for E03
F37

Your boiler has temporarily stopped working because the water pressure inside the heating system has dropped too low.

High DIY-safe

What to check first

  1. Locate the filling loop valves connected to your boiler.
  2. Open the valves gently to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valves tightly and reset the boiler if it does not restart automatically.

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for F37
F40

Your boiler has temporarily stopped working because the water pressure inside your heating system has dropped too low.

High DIY-safe

What to check first

  1. Locate the filling loop underneath your boiler or near the hot water cylinder.
  2. Open the valves slowly to let mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valves tightly and reset the boiler if it does not restart automatically.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Automatic bypass valve

Related codes

Full explanation for F40
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