Your boiler has lost its connection to the solar heating controls, so it has stopped checking in with them, but your main heating and hot water should still work normally.

DIY fix possible

Turn off the boiler at its on/off switch and at the fused spur or isolator for about 2 minutes, then switch it back on and check whether the code clears.Check that the solar controller or Vitosolic display (if you have one) has power and is switched on.If the code returns, stop and contact a Gas Safe registered engineer, as the fault may be a damaged or loose connecting cable that needs checking inside the boiler.