Your boiler is having trouble talking to its add-on internet and remote monitoring unit, but this usually doesn't stop your heating or hot water from working.

DIY fix possible

Find the small Vitocom 100 unit (usually mounted near the boiler or on a wall nearby) and check its status light is on.Switch off the power to the Vitocom 100 at its plug or socket, wait 30 seconds, then switch it back on and wait a few minutes for it to restart.Check that the thin communication cable between the Vitocom 100 and the boiler is firmly plugged in at both ends, and look for any visible damage.Check the boiler display again. If the Cd code returns, contact a Viessmann-registered engineer, as the Vitocom 100 or its cable may need replacing.