Common problems guide

The most common Halstead Ace High problems

The faults most likely to send a Halstead Ace High into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
11 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
Power ON LED (Green) blinking High DIY-safe

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.

What to try first

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

Est. cost
£120-220
Parts
Diverter valve microswitch, Flow switch, Pressure sensor
Full guide for Power ON LED (Green) blinking
02
RED LED ON High Engineer

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.

Est. cost
£120-250
Parts
Ignition Electrodes, Overheat Thermostat, Printed Circuit Board
Full guide for RED LED ON
03
Ignition Lock-out High Engineer

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

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for Ignition Lock-out
04
OVERHEAT THERMOSTAT High Engineer

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

Est. cost
£120-250
Parts
Overheat thermostat, Pump, Diverter valve
Full guide for OVERHEAT THERMOSTAT
05
Safety Lockout LED (Red) High Engineer

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

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for Safety Lockout LED (Red)
06
GREEN LED FLASHING Low DIY-safe

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

What to try first

Turn up your room thermostat to a temperature higher than the current room temperature.Ensure your heating timer or programmer is set to 'On' for the current time.Check that you have not accidentally pressed the 'Off' or 'Summer' mode setting on your boiler controls.

Full guide for GREEN LED FLASHING
Parts most often replaced

on the Halstead Ace High

Diverter valve microswitchFlow switchPressure sensorIgnition ElectrodesOverheat ThermostatPrinted Circuit Board

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Halstead shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 11-code list for the Halstead Ace High

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →