Alpha CB28 Fault codes & diagnostics

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

Combi Natural Gas 28 kW 1997-2005 Discontinued
GC Numbers 47-532-1647-532-17

Replaced by: CB28 Plus

No manual available yet We don't hold the official service manual for this model yet. We're sourcing it — check back soon.

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Just want the most common Alpha CB28 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 3 documented codes

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LED / flash-pattern codes
A Flashing

Your boiler is struggling to accurately read its own internal water temperature, which means it has safely shut down to prevent overheating.

High Engineer only £120-180

Parts commonly replaced

  • NTC Sensor
  • Wiring harness
Full explanation for A Flashing
B Flashing

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Central heating pump
  • Diverter valve
  • Primary heat exchanger
Full explanation for B Flashing
Digital codes
B Illuminated continuously

Your boiler has attempted to start several times but has been unable to successfully ignite its internal flame.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for B Illuminated continuously