BoilerFaultCodesThe 6 most common faults
01
P High DIY-safe
Your boiler is struggling to operate because the electrical supply is unstable or too low, preventing the flame from starting safely.
What to try first
Check if other electrical appliances in your home are flickering or underperformingEnsure the boiler is plugged directly into its fused spur and not an extension leadReset the boiler by turning the control knob to the 'Reset' position for five seconds and then back to 'On'
02
Water flow failure High DIY-safe
Your boiler has stopped because it cannot detect enough water moving through the system to heat safely.
What to try first
Check your boiler pressure gauge to ensure it is sitting between 1 and 1.5 bar.If the pressure is too low, use the filling loop to top up the system.Reset the boiler once the pressure is corrected.
03
1 High Engineer
Your boiler has temporarily shut down because the internal temperature got too high, which is a safety feature to prevent damage.
Full guide for 104
3 High Engineer
Your boiler is trying to start up and light the flame, but it is failing to ignite after five attempts and has safely locked itself out.
Full guide for 305
2 High Engineer
Your boiler has detected an internal sensor or safety check failure and has safely locked itself out to prevent unsafe operation.
Full guide for 206
4 High Engineer
Your boiler has sensed that the exhaust gases are becoming too hot, causing it to shut down automatically for your safety.
Full guide for 4on the Halstead Ace HE
Printed Circuit Board (PCB)External Voltage RegulatorTransformerWater pressure switchCirculating pumpFlow sensor
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