Your boiler has lost its connection to its optional remote-monitoring device, so it can't report its status online, but it will usually keep heating and supplying hot water as normal.

DIY fix possible

Turn off the boiler at its on/off switch and at the fused spur or circuit breaker, wait 2 minutes, then turn it back on.Check that the boiler is still heating and producing hot water, and see whether the Cd code clears on its own after a few minutes.If the code returns, look at the outside of the boiler casing and any remote-monitoring unit to confirm that any visible plugs or cables are fully pushed in. Do not remove any panels or touch wiring inside the boiler.