Alpha CB28 Fault codes & diagnostics

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

Combi Natural Gas 28 kW 1997-2005 Discontinued
GC Numbers 47-532-1647-532-1747-532-1447-532-15

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.

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. 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 4 documented codes

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E01

Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.

High Engineer only £150-300 Shared across the range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E01
E02

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

High Engineer only £120-250 Shared across the range

Parts commonly replaced

  • Pump
  • Diverter valve
  • Primary heat exchanger
  • Limit thermostat

Related codes

Full explanation for E02
E03

Your boiler has detected an issue with the ventilation system that clears away exhaust gases, so it has shut itself down to keep your home safe.

Emergency Engineer only £120-250 Shared across the range

Parts commonly replaced

  • Flue pressure switch
  • Air pressure switch tubing
  • Fan assembly
  • Flue thermostat
Full explanation for E03
E10

Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe £80-120 Shared across the range

What to check first

  1. Locate the external filling loop, which is usually a flexible silver hose connected between two pipes under the boiler.
  2. Open the small valve(s) on the loop to allow water into the system while watching the pressure gauge on the front of the boiler.
  3. Close the valve(s) once the needle reaches the green zone, typically between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor
Full explanation for E10