Error 9U 233

Safety precautions:

- If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency number (or your local emergency gas service) — do not operate electrical switches or the boiler.

- If you attempt any checks, shut the boiler off at its isolator switch or fused spur first. Do not remove the boiler casing or touch internal components unless you are a Gas Safe qualified engineer.

- If you are unsure at any point, or if the boiler has recently had work done, stop and call a Gas Safe engineer.

Initial homeowner checks (safe, non-invasive):

1. Basic reset: try resetting the boiler using the manufacturer’s reset button or by following the reset procedure in the boiler manual (press/reset hold for ~3 seconds or turn the dial to the reset position). Wait and observe whether the fault reappears.

2. Power and controls: check that the boiler is receiving mains power (fused spur not tripped) and that external controls (room thermostat, programmer) are powered and calling for heat. Replace thermostat batteries if applicable and confirm wiring to external controls hasn’t been disturbed.

3. Recent work or changes: note any recent servicing, part replacements or power surges. If someone has recently worked on the boiler, a wrong/replaced HCM or loose connector could be the cause.

4. Visual external check: with the boiler power off, look for obvious signs of water ingress or corrosion at conduit entries or external connectors and ensure the boiler front panel is seated correctly. Do not open the boiler cover.

If the fault persists after the safe checks and reset:

- Do not attempt to open the boiler or probe the PCB or gas circuits yourself. The likely fixes involve checking and reseating or replacing internal modules (HCM/code plug, KIM or burner control unit) and wiring harnesses, which require specialist knowledge and isolation procedures.

What a Gas Safe engineer will do (for your information):

1. Confirm the fault code and any cause code from the boiler information menu (via spanner/return or diagnostics).

2. Isolate gas and electrical supplies and open the boiler safely.

3. Inspect the Heat Control Module/KIM and the code plug: check the seating of the code plug, condition of the plug and its pins, and confirm the correct HCM model for that boiler. Check for loose connectors and damaged wiring or signs of corrosion/water.

4. Verify wiring continuity and correct connections between the burner control unit, HCM/KIM and other modules. Repair any damaged wiring or connectors.

5. If the code plug/HCM or burner control unit is faulty or the wrong part is fitted, replace the defective module with the correct Worcester Bosch part. Reprogramme or initialise the replacement if required by the manufacturer procedure.

6. Clear the fault, recombine panels, restore supplies and test the boiler through a full sequence to confirm normal operation and no further faults.

Final notes:

- Because this fault relates to internal electronics, and because the repair can involve gas isolation and working live or low-voltage electronics, you should call a Gas Safe registered engineer if the reset does not permanently clear the code. Provide the engineer with the exact fault code (9U 233), the boiler model (GB162), and any recent history (service, power cuts, part replacements) to help speed diagnosis.

- Avoid repeated resets if the fault returns immediately; document when it occurred and what you tried, then arrange for professional repair.