Halstead Ace Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2000-2005 Discontinued
GC Numbers 41-333-7747-333-10

Replaced by: Ace High

Download the Halstead Ace 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 →

Severity at a glance

Each cell = one fault code. Hover to identify.
7 High
Just want the most common Halstead Ace faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 7 documented codes

Tap any card for details

LED / flash-pattern codes
Power ON (Green LED) blinking

Your boiler has stopped working because it doesn't have enough water inside the system to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate your boiler's filling loop, which is usually a silver braided hose connecting two pipes under the boiler.
  2. Open the valves on the filling loop to allow cold mains water into the system until the pressure gauge reads between 1 and 1.5 bar.
  3. Close the valves tightly and check the front panel to see if the blinking light has stopped.

Parts commonly replaced

  • Pressure relief valve
  • Flow switch
  • Pressure gauge
Full explanation for Power ON (Green LED) blinking
Digital codes
Activate

Your boiler has failed to ignite and cannot establish a flame, likely because it is not properly recognising its internal control settings or requires a part replacement.

High Engineer only £180-350

Parts commonly replaced

  • BCC (Boiler Control Card)
  • Ignition lead
  • Spark generator
Full explanation for Activate
Ignition Lock-out

Your boiler has stopped working because it failed to light the flame, so it has purposefully shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for Ignition Lock-out
Ignition lockout

Your boiler has stopped working because it failed to light the flame, which often happens due to a simple supply issue or a temporary glitch.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for Ignition lockout
Overheat thermostat

Your boiler has automatically turned itself off because it got too hot, likely to prevent internal damage or overheating.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • Diverter valve
  • System filter
Full explanation for Overheat thermostat
Safety Lock-out LED

Your boiler has stopped working because it failed to light or has become too hot, causing a safety shutdown to protect your home.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Overheat thermostat
  • Printed Circuit Board (PCB)
Full explanation for Safety Lock-out LED
Safety Lockout (Red LED)

Your boiler has stopped working because it failed to start, which could be due to a simple supply issue or a more complex internal fault.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)
Full explanation for Safety Lockout (Red LED)
Status & diagnostic codes

3 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

C (Flashing) Status Your boiler has accidentally switched into a low-power maintenance mode meant only for technicians, meaning it is currently providing much less heat than usual. F4 Diagnostic Your boiler has stopped working because an internal safety fuse on the main control board has blown, cutting off the power required to operate the unit. Power On LED Status Your boiler is operating normally and is currently set to provide hot water to your taps or shower.