Error 9A 362

Safety precautions:

- Do not attempt internal electrical or gas repairs unless you are a registered Gas Safe engineer.

- Before any basic checks isolate the boiler by switching off at the mains or using the boiler’s appliance switch and turn off the gas supply if instructed by a professional.

- Keep children and pets away from the appliance while inspecting it.

Initial homeowner checks (safe, non-intrusive):

1. Note exactly when the error appeared and any recent work on the boiler (servicing, part replacements, power outages, or upgrades). Record the full fault display (9A 362) and any additional codes or messages.

2. Check the boiler has power: confirm the household supply and the boiler’s fused spur or plug (if fitted). If the boiler is dead, call an engineer.

3. Try a reset: follow the boiler’s reset procedure (press the reset button or use the control panel). Wait a minute and see if the fault returns. If it clears and stays cleared, monitor the boiler; if it reappears, stop and call a professional.

4. Look for evidence of recent service: a work sticker, service tag, or part replacement note. If a non-authorised engineer or DIYer recently worked on the unit, tell the attending engineer.

5. Do not remove the outer casing or access internal electronics unless you are competent and qualified; this can void warranty and is potentially dangerous.

Diagnostic and fix steps (for a qualified heating engineer):

1. Confirm the fault using the boiler diagnostics and fault history. Note any related codes (eg 9U, B1) which may indicate code plug or control box problems.

2. Visually inspect the control box area: check HCM seating, connectors, plug pins, and the code plug for signs of incorrect part numbers, damage, corrosion or poor connection. Reseat connectors and code plug if necessary and re-check fault memory.

3. Verify part numbers and compatibility: check the boiler model/rating, KIM and code plug version against Worcester Bosch parts catalog to confirm the correct HCM for that appliance. An incorrect HCM often comes from fitting a part intended for a different model or firmware revision.

4. If the HCM or code plug is incorrect, replace it with the correct OEM HCM/code plug matched to that boiler model. If the control box and HCM are incompatible, the control box (burner control unit/PCB) may also need replacement or reprogramming to match the HCM.

5. After replacement or reseating, perform commissioning checks: run the built-in tests (ignition, fan, pump, sensor tests), clear fault memory, and cycle the boiler through CH and DHW demands to confirm normal operation and that no further compatibility faults exist.

6. Check for any secondary faults caused by previous incorrect fitment (wiring damage, sensor faults, lockouts) and resolve them before returning the appliance to service.

7. Complete documentation: record the fault, parts replaced, and tests performed on the service record, and advise the homeowner of what was done.

When to call a professional:

- If the reset does not clear the fault or it returns, stop attempting more intrusive work and call a Gas Safe registered engineer.

- Any internal inspection, HCM removal or replacement, control box replacement, or reprogramming must be carried out by a qualified engineer due to safety and gas regulations.

Additional notes:

- Sometimes the fault is caused by a loose connector or a knocked code plug; reseating can clear the error, but only an authorised engineer should open the casing.

- Provide the engineer with as much information as possible (error code, boiler model and serial, any recent work) to speed diagnosis.

- Do not attempt to bypass safety interlocks or to fit non-genuine/incorrect control modules yourself; this creates safety and legal risks and may invalidate warranties.