Alpha CD C Fault codes & diagnostics

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

Combi Natural Gas 25-35 kW 2013-2018 Discontinued

Replaced by: E-Tec

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 CD C 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
Neon A flashing

Your boiler is struggling to circulate water properly, which means it has stopped heating your home to prevent potential internal damage.

High Engineer only £150-350

Parts commonly replaced

  • Circulation pump
  • Flow switch
  • System filter

Related codes

Full explanation for Neon A flashing
Neon B flashing

Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • Diverter valve
  • PCB
Full explanation for Neon B flashing
Digital codes
Neon D NOT illuminated

Your boiler has no power, meaning it cannot start up to provide heating or hot water because it is not receiving any electricity.

High DIY-safe £100-300

What to check first

  1. Check your consumer unit to see if the boiler's circuit breaker has tripped
  2. Ensure the fused spur switch located near the boiler is turned on
  3. Check the fuse inside the fused spur switch to see if it has blown

Parts commonly replaced

  • Fused spur switch
  • PCB (Printed Circuit Board)
  • Wiring harness
Full explanation for Neon D NOT illuminated