Alpha CB50 Fault codes & diagnostics

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

Combi Natural Gas 50 kW 2007-2016 Discontinued
GC Number 47-532-18

Replaced by: E-Tec Plus 38

Download the Alpha CB50 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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 →

All 3 documented codes

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A Flashing

Your boiler's internal thermometer is failing to send reliable signals, so the system has shut down to prevent it from overheating.

High Engineer only £120-220

Parts commonly replaced

  • NTC Thermistor
  • PCB

Related codes

B Flashing

Your boiler has detected that it is getting too hot and has automatically shut down to prevent any damage or safety hazards.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • Diverter valve
  • Heat exchanger
B Illuminated continuously

Your boiler has stopped working because it failed to ignite the gas burner, meaning you will currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB