Halstead Ace High Fault codes & diagnostics

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

Combi Natural Gas 20 kW 2006-2010 Discontinued

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.
5 High 6 Low
Just want the most common Halstead Ace High faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 11 documented codes

Tap any card for details

LED / flash-pattern codes
GREEN LED FLASHING

Your boiler is perfectly healthy and is simply waiting for a signal from your thermostat or hot water tap to start heating.

Low DIY-safe

What to check first

  1. Turn up your room thermostat to a temperature higher than the current room temperature.
  2. Ensure your heating timer or programmer is set to 'On' for the current time.
  3. Check that you have not accidentally pressed the 'Off' or 'Summer' mode setting on your boiler controls.
Full explanation for GREEN LED FLASHING
Power ON LED (Green) blinking

Your boiler has detected that there is either not enough water inside the heating system or the sensor responsible for detecting flow is not operating correctly.

High DIY-safe £120-220

What to check first

  1. Check your boiler's pressure gauge and ensure it is between 1 and 1.5 bar.
  2. If the pressure is low, locate the filling loop under the boiler to top up the system.
  3. Once the pressure is correct, restart the boiler to see if the blinking light stops.

Parts commonly replaced

  • Diverter valve microswitch
  • Flow switch
  • Pressure sensor
Full explanation for Power ON LED (Green) blinking
Digital codes
Ignition Lock-out

Your boiler has stopped working because it cannot light the flame required to produce heat or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB
Full explanation for Ignition Lock-out
OVERHEAT THERMOSTAT

Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent any damage or safety issues.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • Diverter valve
  • System filter
Full explanation for OVERHEAT THERMOSTAT
Power ON LED (Green)

Your boiler is working perfectly fine and is simply waiting for you to turn on a tap or adjust your heating settings.

Low DIY-safe

What to check first

  1. Check your room thermostat is set to a higher temperature than the current room temperature.
  2. Ensure the timer or programmer is set to 'On' or 'Timed'.
  3. Check that the hot water demand is active by opening a tap.
Full explanation for Power ON LED (Green)
RED LED ON

Your boiler has stopped working because it has failed to start properly or has become too hot and turned itself off as a safety precaution.

High Engineer only £120-250

Parts commonly replaced

  • Ignition Electrodes
  • Overheat Thermostat
  • Printed Circuit Board
Full explanation for RED LED ON
Safety Lockout LED (Red)

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

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB
Full explanation for Safety Lockout LED (Red)