Alpha HETEC Fault codes & diagnostics

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

Combi Natural Gas 25 kW Discontinued
Choose your boiler type

The HETEC range comes in 3 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

HE SY25 0 codes · 1 GC number HE CB25 0 codes · 1 GC number HE CB33 0 codes · 1 GC number
Each model has its own manual A family spans several manuals, one per model or generation. Pick your model above and its page has the manual its fault codes were read from.

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.
2 Emergency 4 High 2 Low
Just want the most common Alpha HETEC 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 alternatively

Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.

High DIY-safe Shared across the Alpha HE range

What to check first

  1. Locate the filling loop under your boiler or near the hot water cylinder.
  2. Open the valves slowly to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valves firmly and check the boiler display or reset the unit if necessary.

Parts commonly replaced

  • Filling loop valve
  • Pressure relief valve
  • Pressure gauge

Related codes

Full explanation for Neon A and B Flashing on and off alternatively
Neon A and B Flashing on and off at the same time

Your boiler has detected an issue with safely removing exhaust gases outside, so it has locked itself out to prevent any risk.

Emergency Engineer only £150-350 Shared across the Alpha HE range

Parts commonly replaced

  • Flue fan
  • Air pressure switch
  • Flue terminal
Full explanation for Neon A and B Flashing on and off at the same time
Neon A Flashing on and off

Your boiler has automatically shut down because it detected dangerously high temperatures inside the unit.

Emergency Engineer only £150-300 Shared across the Alpha HE range

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • PCB
Full explanation for Neon A Flashing on and off
Neon B Flashing very slowly (every 5 seconds)

Your boiler is receiving power normally and is currently in standby mode waiting for a heating or hot water demand.

Low DIY-safe Shared across the Alpha HE range

What to check first

  1. No action is required as this is a normal operational status light indicating the boiler is powered on.
Full explanation for Neon B Flashing very slowly (every 5 seconds)
Digital codes
Neon A Illuminated continuously

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

High Engineer only £150-300 Shared across the Alpha HE range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for Neon A Illuminated continuously