Error B1

Safety precautions:

1) Before you start, switch the boiler off at the main switch and isolate electrical power at the fused spur or consumer unit. Do not work inside the boiler with power connected. If you smell gas or suspect a gas leak, leave the property and contact the gas emergency service immediately.

2) Do not tamper with gas valves, burner components or wiring unless you are a Gas Safe qualified engineer. Removing covers for a visual inspection is acceptable if you follow the manufacturer’s instructions and have isolated power.

Initial checks a homeowner can do:

1) Note the boiler model and the exact fault code (B1). Also check the information/cause code by pressing the spanner/return or info button on the boiler control panel if your model shows a cause code—record it for the engineer.

2) Try a basic reset: follow the boiler’s reset procedure (press the reset button or hold the dial to the reset point for 3 seconds). If the B1 comes back immediately or after a restart, further investigation is needed.

3) Check the boiler display and any flashing lights for additional information (locking/locking triangle), and check that external controls (room thermostat, timer) are not causing a lockout.

Specific diagnostic and fix steps (visual inspection and reseating only):

1) Isolate power to the boiler and wait a minute for capacitors to discharge.

2) Remove the front casing/panel following the manufacturer’s instructions so you can see the PCB and associated modules. Keep screws safe. Do not remove flue components or gas fittings.

3) Locate the code plug: it is a small plastic plug/module inserted into a socket on the control board or HCM. It may be a different colour to the PCB and may be labelled on the board or in the manual.

4) Inspect the code plug and socket: look for corrosion, dirt, bent pins, burn marks or signs of damage on the plug and the PCB socket. Also check the wiring harness and nearby connectors for secure fit and no damage.

5) If the plug is present and looks seated, carefully withdraw it (note its orientation) and inspect the contacts. Gently clean any visible dirt or corrosion with a dry cloth or contact cleaner rated for electronics (only if you are comfortable doing so). Refit the plug firmly so it is fully seated.

6) Refit the boiler casing, restore power and test: switch the boiler on and check whether B1 clears. If the code clears and the boiler runs normally, monitor for recurrence and report to your service engineer at the next opportunity.

If the plug was missing or damaged:

1) Do not fit an unknown or incorrect code plug. The code plug must match the boiler model and configuration. Contact the original installer or a Gas Safe engineer to supply and fit the correct code plug.

If reseating/replacing the visible plug does not clear the fault or the plug looks fine:

1) The issue may be a faulty code plug, damaged socket on the PCB/HCM, a wiring fault, or a PCB/HCM fault. These are not safe DIY repairs. Take note of any cause codes or additional fault numbers shown in the information menu and provide them to the engineer.

2) Call a Gas Safe registered Worcester Bosch-trained engineer to diagnose and replace the code plug, HCM or PCB as required. Give the engineer the boiler model, serial number and the B1 (and any cause) codes you recorded.

When to call an engineer immediately:

1) If reseating the plug does not help and the boiler remains locked out; or you see additional fault codes or signs of electrical damage; or if you detect gas smell or leaks; or if you are not confident to remove the casing.

2) If the fault returns repeatedly after reseating, do not keep resetting the boiler. Get a professional to avoid unsafe operation.

Information to give the engineer:

1) Boiler model and serial number, the B1 error and any three-digit cause code from the information menu, a description of what you tried (reset, reseat plug), and whether the code plug was missing/damaged or sockets looked corroded.

Final note:

Basic visual checks and reseating the code plug are reasonable for a competent homeowner after isolating power, but any replacement of modules, PCB/HCM, or work involving gas or live wiring must be done by a Gas Safe registered engineer. Do not attempt to jury-rig or fit an incorrect code plug.