Error 1 long flash, 4 quick flashes, 5 second gap, 1 long flash, 4 quick flashes

Safety precautions:

- If you are not qualified, do not open or attempt to repair gas or electronic components beyond basic visual checks and resets.

- Before doing any work on the boiler’s internals, switch off electricity to the boiler at the consumer unit and, where available, isolate the boiler at its fused spur. Do not touch live parts.

- If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency number. Do not operate electrical switches.

Initial checks a homeowner can do safely:

1) Record exactly when the fault occurred and the exact flash sequence. Note any recent events (power cut, storms, service work, component replacement).

2) Try a simple reset first: follow the manual for your model — press the reset/spanner button for about 3 seconds or turn the control knob to the reset position and hold for 3 seconds. Wait and observe whether the boiler restarts and runs normally or if the same fault returns.

3) Power-cycle the boiler: switch off at the boiler fused spur or consumer unit, leave off for 60 seconds, then restore power and check the behavior.

4) Check the mains supply and household fuses/RCDs to ensure the boiler is receiving stable power. Note any recent power interruptions.

5) Check boiler display and any static cause code or warning triangle, and check boiler pressure and visible condensate pipe for obvious blockages or freezing (these are not the HCM but are quick checks).

Specific diagnostic checks (visual, non-invasive):

1) With the boiler powered off at the consumer unit and allowed to discharge, remove the outer casing only if you are comfortable doing so and the boiler instructions allow it. Some warranty terms may be affected by user access — if in doubt, stop and call an engineer.

2) Inspect the HCM area and main control board for signs of water ingress, corrosion, loose or disconnected connectors, burnt components or smell of burning. Pay attention to cable plugs between the HCM and main PCB and the code plug area if fitted.

3) Reseat any accessible, keyed plugs and connectors (only when mains is off). Ensure connectors clip fully home and there are no bent pins. Make a note which connectors you touch so you can restore them correctly.

4) Check the code plug/module (if present) is fitted correctly and not damaged. Some HCM errors are caused by an incorrect or missing code plug or the wrong HCM being fitted after repair.

5) Restore power and see if the fault reappears. If the fault returns immediately and consistently, it points to an HCM internal fault, incorrect HCM, or persistent wiring/connector issue.

If the above steps do not clear the fault:

- Do not attempt to bypass or bridge any safety circuits. The HCM governs ignition, fan and safety sensors and bypassing is dangerous and illegal.

- Contact a Gas Safe registered engineer or Worcester Bosch service agent. Tell them the exact flash sequence, what checks you have already completed, and whether the fault returned after a reset or power-cycle. Mention any visible signs you found (water, corrosion, loose plugs, missing code plug) and any recent power cuts or work on the boiler.

What a professional will likely do:

- Run full diagnostic checks, review fault logs and perform sensor and wiring tests with the proper test equipment.

- Confirm whether the HCM itself is faulty, whether an incorrect HCM or code plug is fitted, or whether a wiring/connector issue is causing the HCM to be not recognised.

- Replace or reprogram the HCM and fit the correct code plug if required, then test the boiler through full operating cycles. Only a qualified engineer should fit or replace the HCM because it must be matched correctly and the repair involves working on gas and combustion components.

Additional notes and evidence for the engineer:

- Keep a clear record of fault timings, reset attempts and any environmental events (power cuts, storms) and whether the boiler has been recently serviced or components replaced. This helps reduce diagnostic time.

- If the boiler is under warranty or service plan, contact the manufacturer or service provider first and do not attempt repairs that might void coverage.

Summary: perform safe, non-invasive checks and a reset first. If the fault persists the HCM or related wiring/connectors is likely defective and a Gas Safe qualified engineer should be called to diagnose and replace/reprogram the module.