Error B1

Safety precautions:

- If you smell gas, evacuate the property and call the gas emergency number immediately. Do not attempt any checks.

- Before opening the boiler case or touching internal parts isolate the electrical supply at the fused spur or consumer unit and switch the boiler off. If you are not confident working with electrical equipment do not open the appliance.

- Do not tamper with gas controls, burners or sealed components. Only a Gas Safe engineer should work on gas-tight or combustion parts.

Initial homeowner checks (safe, simple steps):

1. Try a boiler reset: press and hold the reset button for about 3 seconds (or use the reset position as described in your manual). Wait a minute and see if the error returns. A single reset is fine; repeated resets without progress are not advised.

2. Check whether the error appeared right after a service, part replacement or power cut. If a service was recently done, a plug may have been left unseated.

3. Make a note or photo of the display showing B1 and any additional cause code shown in the information menu (press the spanner/return button if your control panel supports it). This information is useful for an engineer.

If you are comfortable and competent with basic appliance checks (only if isolated from mains):

1. Isolate the boiler electrically at the boiler switch or fused spur. Confirm power is off.

2. Remove the outer case following the manufacturer's instructions (if you are not sure how, stop here and call an engineer). Take care not to force clips and keep screws organized.

3. Locate the main PCB / control module area. The code plug is usually a small plastic plug or identification module which plugs into the main PCB or the HCM/KIM module. It may be labelled or look like a small ROM or plastic connector.

4. Visually inspect the code plug and its socket for signs of looseness, corrosion, bent pins, burn marks, water ingress or damaged wiring. Also check the surrounding wiring harness and multi-pin connectors for secure seating.

5. If the plug appears seated but you can safely do so, carefully unplug and re-seat the code plug (pull straight out, avoid twisting). Ensure it is fully pushed back into its socket. If any connector clips or locking tabs are present, make sure they engage.

6. Re-assemble the cover, restore power and try a reset. Check whether the B1 clears and whether the boiler returns to normal operation.

If the fault persists or you are unable/unwilling to open the boiler:

- Power-cycle the boiler (turn off, wait 30 seconds, turn on) and try reset once more. If B1 returns, stop further DIY attempts.

- Photograph the code plug area, the PCB label, and any connectors or damage and provide these to the engineer.

- Contact a Gas Safe registered Worcester Bosch–competent engineer. Explain the B1 code and the steps you have already taken and provide photos and any cause code from the info menu. The engineer will test the plug/socket, check PCB communications, and replace the code plug or control module if required.

Important notes and when to call a professional:

- Replacing the code plug or PCB, diagnosing PCB faults, or doing any work that involves gas or combustion components must be done by a Gas Safe registered engineer. If re-seating the plug and a single reset do not clear the fault, call a professional.

- Do not attempt to operate the boiler repeatedly if it keeps locking out; repeated attempts can mask a deeper fault and create unsafe conditions.

- Keep records of error codes, photographs and service history to speed up the engineer’s diagnosis.

Summary: Try a single reset and a safe visual check or re-seat of the code plug only if you are competent and have isolated the power. For any replacement of modules, internal electronic faults or if the error remains, book a Gas Safe engineer to diagnose and repair.