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

Safety precautions:

1) If you smell gas or suspect a leak, evacuate the property immediately and call the gas emergency number. Do not operate electrical switches or the boiler.

2) Before attempting any checks on the boiler internals, isolate the electrical supply at the fused spur or consumer unit and if you intend to expose internal components you must be qualified. Do not open the boiler case or touch internal components unless you are trained and Gas Safe registered.

3) Do not repeatedly force resets or run the boiler if it behaves unpredictably.

Initial homeowner checks (safe, no internal access required):

1) Note and record the exact flash sequence and any other indicators on the display. Take a photo if helpful.

2) Try a single controlled reset: turn the boiler control knob to the reset position or follow the manufacturer reset procedure once. Wait for the boiler to attempt a restart. If the fault returns immediately or after a short period, do not keep resetting.

3) Check the mains power to the boiler (fuse spur is on, other appliances working). If you have had a recent power cut or surge, a reset may temporarily clear errors but the underlying board fault can reoccur.

4) Check the boiler pressure gauge and visible pipework for leaks or standing water under the boiler (leaks can cause corrosion and PCB faults). If pressure is very low or there is visible leakage, isolate the boiler and contact an engineer.

5) Ensure external controls (room thermostat, programmer, smart control) are working and batteries are ok. Remove external control demand briefly to see if the boiler behaves differently.

6) Check the condensate pipe (if weather cold) only externally for visible freezing or blockage; a blocked condensate can cause other faults but not usually a direct PCB error.

If you are comfortable with basic, safe isolation and external connector checks (only if competent):

1) Isolate mains power at the fused spur and leave off while performing any connector inspection. Do not work live.

2) With power isolated, inspect the boiler exterior and any visible wiring to the boiler for signs of burning, water ingress, corrosion, rodent damage or loose plug-in connectors. Do not probe PCB connectors unless you are trained. Tighten loose external connectors (not internal PCB screws) if they are obviously loose and accessible.

3) If you find clear signs of water ingress, corrosion, burn marks or a damaged wiring harness, do not power up. Photograph the damage and call a Gas Safe engineer.

What a professional will do / when to call a Gas Safe engineer or Worcester Bosch support:

1) If the simple reset does not clear the fault, or the fault reappears, contact a Gas Safe registered engineer. State the exact flash sequence and any other observations (smell of gas, visible damage, recent power cuts, water ingress). This code points to an internal control board issue that usually needs professional fault-finding and often replacement of the PCB or related module(s).

2) The engineer will perform controlled diagnostic tests: check supply voltages, earths, connectors and wiring, run service diagnostics from the boiler’s service menu, test sensors and actuators the PCB controls (fan, pump, gas valve, ionisation/flame sensing), and check for transient faults caused by power supply problems or failed peripheral components.

3) If the control board is faulty, a qualified engineer will replace it and carry out commissioning, gas-safety checks and function tests. They will also check for underlying causes (water leaks, corrosion, poor ventilation, or other failed components) that might have damaged the board.

Important notes and final advice:

1) Do not attempt board-level repairs, soldering or component replacement on gas appliances unless you are a qualified appliance engineer. Unauthorized repairs are dangerous and illegal in many regions.

2) Keep a record of the fault sequence, any resets you attempted, and any visible symptoms to pass to the engineer. If the boiler is under warranty or service contract, contact Worcester Bosch or your service provider and provide the fault details.

3) Treat this as a priority repair if you rely on the boiler for heating/hot water, but only allow a Gas Safe engineer to carry out internal repairs, replacements and final testing.