BoilerFaultCodes Neon A and B Flashing on and off alternatively
System pressure is very low and re-pressurisation is required.
Alpha CD28 Fault codes & diagnostics
8 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
CombiSystem Natural Gas 28 kW 2007-2012 Discontinued
GC Numbers 41-532-0241-532-0641-532-0847-532-1647-532-1747-532-1947-532-21
Replaced by: CD28C
Download the Alpha CD28 manual
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 →
Severity at a glance
Each cell = one fault code. Hover to identify. 8 Unrated
Just want the most common Alpha CD28 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 8 documented codes
Tap any card for details
LED / flash-pattern codes
Neon A and B Flashing on and off at the same time
Blocked flue or fan fault.
Neon A Flashing on and off
Overheat thermostat has operated. Rotate selector switch to the reset position (3) to reset.
Neon B Flashing (every 5 seconds)
Electricity supply to the boiler is on.
Neon B Flashing on and off
Temperature sensor fault.
Neon B Flashing very slowly (every 5 seconds)
Electricity supply to the boiler is on.
Digital codes
Neon A Illuminated continuously
Burner has failed to light. Rotate the selector switch to the reset position (3) and the ignition sequence will restart after a delay of about 30 seconds.
Neon B Illuminated continuously
Indicates the burner is alight.