Error F0 238

Safety precautions:

1) If you smell gas: do not operate electrical switches, open windows and doors, leave the property immediately and call your local gas emergency number (in the UK call 0800 111 999) and a Gas Safe engineer. 2) If you suspect carbon monoxide (CO) exposure — headaches, nausea, dizziness, yellow flames, sooting — turn off the appliance, leave the property and seek fresh air and medical help. 3) Do not attempt to dismantle the gas valve, burner control box, or the KIM module yourself unless you are a qualified Gas Safe engineer. Live gas and mains electricity are hazardous.

Initial homeowner checks you can safely perform:

1) Record the fault: write down or photograph the exact fault display (F0 238) and any cause code shown on the boiler display or info menu. This helps the engineer. 2) Power and supply check: confirm the boiler has mains power and the boiler isolator/fuse is on and the house hasn’t tripped any RCDs. 3) Gas supply check: verify other gas appliances in the house are working. If all gas appliances are off, check the house gas meter/valve is on. If you suspect a supply issue, contact your gas supplier. 4) Water pressure: check the boiler pressure is in the normal range (typically about 1.0–1.5 bar). Low pressure can cause unrelated lockouts — top up only if you know how to do this safely. 5) Single reset: follow the manual’s reset procedure (press/reset button for ~3 seconds or use the reset position on the temperature knob). Do a single reset only and then observe — do not repeatedly reset a locking fault.

Visible, non-invasive inspection (homeowner):

1) Look for visible signs of damage or water ingress on the boiler outer casing or control panel (wetness, corrosion, burn marks) and for any loose external connectors you can see without removing safety covers. 2) Note any unusual noises, smells, or visible flames when the boiler attempts to fire. 3) Photograph any findings for the servicing engineer. Do not remove internal covers or probe wiring terminals.

Diagnostic and fix steps that a qualified engineer will typically perform (for information):

1) Access service menu and read full fault and cause codes and event log. 2) Inspect the burner control unit/KIM and control box for water damage, corrosion, burn marks or loose plugs. 3) Check continuity and resistance of gas valve coils and compare with manufacturer specs. 4) Check for gas valve leaks and ensure the valve seats and seals are sound. 5) Test ignition sequence and flame sensing circuitry; check ionisation/flame signal and ignition transform and electrodes. 6) Verify wiring and connectors between the KIM, main PCB/HCM and gas valve; replace any damaged leads or connectors. 7) If the KIM/burner control unit is confirmed faulty, replace it with the correct part number for the GB162 and ensure any code plug / HCM compatibility is correct. 8) If replacement of the gas valve or PCB is required, fit the correct Worcester Bosch parts, perform gas tightness test, set up and run through commissioning steps, and verify safe operation and correct modulation. 9) Re-run diagnostics and clear the fault; observe multiple burner cycles to ensure the issue is resolved.

Important notes and final advice:

1) Because this fault affects the gas control/ignition safety chain, you must call a Gas Safe registered heating engineer to diagnose and repair the appliance. The engineer can safely test the gas valve coils, carry out leak tests and replace control modules and re-commission the boiler. 2) Do not repeatedly reset the boiler; repeated resets can mask a developing hazard and will not fix an electronic or gas valve fault. 3) Make a note of the fault code, any symptoms, and the checks you performed before the engineer arrives — this saves time. 4) If you detect a gas leak or CO risk at any time, evacuate and call emergency services and your gas emergency line immediately.