Error 3 long flashes, 4 quick flashes, 5 second gap, 3 long flashes, 4 quick flashes

Safety precautions:

- If you smell gas, leave the property immediately and call the gas emergency number. Do not switch electrical items on or off.

- Before touching any electrical parts, isolate the boiler at the fused spur or the consumer unit. If you are not competent with mains electricity, do not open or work on the boiler electrical connections — call a qualified electrician or Gas Safe engineer.

- Do not remove panels or attempt gas or combustion-related repairs unless you are a Gas Safe registered engineer.

Initial checks a homeowner can do (no tools beyond simple household checks):

1) Note and record the flash pattern and any alphanumeric cause code shown on the display (press the spanner/return button to view cause codes if available). Take a photo for an engineer.

2) Check if other electrical appliances in the house are working to confirm if you have a general power cut. If other appliances are out, contact your electricity supplier.

3) Check the consumer unit (fuse box) for any tripped MCB or RCD that may have cut power to the boiler. If a breaker has tripped, reset it once and see if power remains stable.

4) Check the boiler fused spur (if accessible) to see if the fuse is blown. Replace the fuse only with the correct rating if you are comfortable doing so.

5) Confirm that any external controls (room thermostat, programmer/timer, smart controller) are powered and calling for heat — sometimes an external control fault can appear alongside power issues.

Simple reset procedure:

1) If mains power is available and you have performed the initial checks, try clearing the lockout: either press the boiler reset button for about 3 seconds or turn the control knob anti-clockwise to the reset position (follow the label on your boiler front panel). Wait and observe the lights and display.

2) After reset, watch the boiler for a few minutes. If it starts and runs normally, monitor for reoccurrence over the next few hours.

3) If the lockout returns immediately or the same flash pattern appears again, do not repeatedly reset the boiler. Repeated resets can mask the underlying problem and may stress components.

Further diagnostic checks (if you are competent with basic observation but not electrical/gas repairs):

1) Check for any other fault codes shown in the information menu (press the spanner/return button) and note the three-digit cause code. These codes give more detail about the original locking error and will help an engineer diagnose the root cause.

2) Look and smell for signs of electrical damage (burn marks, melted insulation) around the boiler fuse spur and wiring. If you see any, isolate power and call a professional.

3) If the consumer unit trips repeatedly when power is restored, stop and call a qualified electrician — do not keep resetting; that indicates a persistent electrical fault.

4) If the mains supply to your property appears unstable (flickering lights, other appliances intermittently losing power), contact your electricity supplier to investigate supply-side issues.

When to call a professional (and what to tell them):

- Call a Gas Safe registered engineer if: the original lockout cause code relates to flame detection, gas valve, ignition, over-temperature, sensor faults, or if the boiler will not reset or repeatedly locks out after reset.

- Call a qualified electrician if: the boiler fused spur shows damage, the consumer unit trips on resetting, or you suspect a loose or damaged mains supply or wiring to the boiler.

- Provide the engineer with: the exact boiler model (Worcester Bosch CDi Highflow Combi), the full flash sequence, any cause code or alphanumeric error code from the display, whether the fuse/MCB/RCD tripped, and what you already tried (reset, fuse check, breaker reset).

Important final notes:

- Don’t attempt to replace or repair gas valves, ignition electrodes, PCB boards, or internal wiring yourself — these are gas or mains electrical tasks that must be done by qualified professionals.

- If a reset temporarily clears the fault but it reappears, arrange an engineer visit; intermittent mains problems or a failing control board can cause repeated lockouts and will need professional diagnostics and repair.

- If in any doubt about safety or the nature of the fault, stop troubleshooting and contact a Gas Safe engineer and/or a registered electrician.