Halstead Ace Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2000-2005 Discontinued

Replaced by: Ace High

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.
4 High 1 Medium 1 Low
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 6 documented codes

Tap any card for details

LED / flash-pattern codes
C (Flashing)

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.

Medium Engineer only £90-180

Parts commonly replaced

  • Main PCB
  • Service switch
Full explanation for C (Flashing)
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
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
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)