Glow-worm Jaguar 28 Fault codes & diagnostics

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

Combi Natural Gas 2000-present
GC Number 47-047-17
Download the Glow-worm Jaguar 28 manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Fault codes

All 5 documented codes

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F0

Your boiler has detected that the water pressure inside your heating system has dropped too low to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, which is usually a small silver braided hose with one or two valves located underneath the boiler.
  2. Open the valve(s) slowly to allow mains water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close the valve(s) tightly and check that the boiler restarts.

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Filling loop

Related codes

Full explanation for F0
F1

Your boiler is trying to start, but it cannot detect a flame, so it has safely shut itself down to prevent gas from building up.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for F1
F2

Your boiler has lost the ability to monitor the temperature of the water circulating to your radiators, so it has shut down to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • NTC Thermistor
  • Wiring harness

Related codes

Full explanation for F2
F3

Your boiler has detected that water is struggling to flow through its internal heating system, likely due to a build-up of sludge or debris.

High Engineer only £180-350

Parts commonly replaced

  • Plate heat exchanger
  • Diverter valve
  • System filter

Related codes

Full explanation for F3
F4

Your boiler is struggling to accurately measure the temperature of the water being heated for your taps, which is preventing it from providing hot water correctly.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC thermistor
  • Wiring harness

Related codes

Full explanation for F4
Status & diagnostic codes

9 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

n1 Diagnostic Your boiler is failing to light the burner because it cannot detect a flame, meaning you will currently have no heating or hot water. n2 Diagnostic Your boiler is not detecting that the pilot light has successfully ignited, so it has shut down to prevent gas from escaping. n3 Diagnostic Your boiler has detected an issue with the sensor that monitors the water temperature or flow, causing the system to stop working correctly as a safety precaution. n4 Diagnostic Your boiler has detected an issue with the water flow or pressure sensor, meaning it has temporarily stopped working to protect the internal components. n5 Diagnostic Your boiler has detected an issue with the sensor that monitors the internal water temperature or flow, meaning it cannot safely heat your water. n6 Diagnostic Your boiler is failing to light the flame properly, which means it cannot produce hot water or heating. n7 Diagnostic Your boiler is failing to detect the flame needed to ignite, which means it cannot produce hot water or heating. n8 Diagnostic Your boiler has detected an issue with its internal airflow or exhaust system, causing it to shut down for safety reasons. n9 Diagnostic Your boiler has detected a failure to ignite, meaning it is currently unable to start up to provide you with heating or hot water.
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