Error 9U 233

Safety precautions:

1) If you are in any doubt, do not open the boiler. Gas and mains electricity are inside the casing; work on them should only be carried out by a Gas Safe registered engineer.

2) Before any visual checks, turn off the boiler using the front controls and isolate the electrical supply at the fuse switch or consumer unit if you are going to access the casing. Do not attempt to isolate or work on the gas supply unless you are qualified.

3) Keep children and pets away while you inspect the appliance. Take photographs of any displays or labels to show an engineer.

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

1) Note the exact fault display and cause code. If the display shows "9U 233" and a triangle, press and hold the reset button for 3 seconds to attempt a reset. Some Worcester boilers require holding reset briefly to clear a locking code.

2) After reset, wait and see if the boiler attempts to restart. If the fault clears and the boiler runs, monitor it and consider booking a service to check the root cause.

3) Check the boiler has mains power and the supply switch is on. Check your house fuses. Some codes are caused by intermittent power or a brief outage.

4) Check whether any recent work has been carried out on the boiler (service, replacement parts). If an HCM or PCB was recently fitted, tell the engineer; an incorrect or incompatible HCM is a common cause.

5) Use the boiler's quick-info/menu (spanner or return button) to view the cause code and take a clear photo of the screen to give to your engineer.

If the fault persists and you are a competent person comfortable with basic checks (ONLY if you understand the risks and after isolating mains power):

1) Isolate mains power at the consumer unit and wait a minute. Remove the outer casing only if you are confident and the manual shows how to do this safely. If you are not confident, stop here and call an engineer.

2) With power isolated and the casing off, visually inspect the HCM and nearby connectors. The HCM is a small control module/box that plugs into the main control PCB and may have a small ‘code plug’ or identifying connector. Look for obvious signs: loose connectors, plastic code plug missing, broken or unseated connectors, or physical damage to wiring.

3) If a connector appears loose and you are certain power is isolated, gently reseat the connector until it clicks. Do not force components.

4) Replace the casing, restore mains power and try a reset on the boiler. If the 9U 233 does not return, monitor operation; if it recurs, leave the boiler off and call an engineer.

When to call a professional and what to tell them:

1) Call a Gas Safe registered Worcester Bosch competent engineer if the fault does not clear after a reset, if you find a damaged or missing code plug or HCM, if connectors are corroded or broken, or if you do not feel safe performing the internal checks.

2) Provide the engineer with the exact fault code (9U 233), the cause code shown in the info menu (if available), and any photos you took of the display and internal connectors. Mention any recent work or part changes.

3) Ask the engineer to check HCM compatibility, reseat/replace the code plug or HCM if defective, and verify full system operation including reset and clearing of the locking code. The engineer will also check for underlying causes (incorrect module fitted, faulty control PCB, wiring issues) and perform a safe repair.

Final notes:

Do not attempt to replace the HCM, PCB or perform gas adjustments yourself unless you are a qualified Gas Safe engineer. Incorrect replacement or installation of electronic control modules can cause further faults or unsafe operation. If the boiler is locked out and the simple reset does not work, arrange a professional service promptly so the correct module and wiring can be verified and repaired.