Vailant Ecotec Plus 837 Radiator heating issue. fault 22?

Hi I recently replaced my old boiler with a new Vailant 837 combi and my heaters dont seem to be heating up, the tap water is brilliantly hot and works perfect.

The LCD on the boiler is showing a F.22 fault which is apparently a dry fire according to the manual but I cant decrypt the instructions on how to fix the problem.

The radiators are warming up but very slightly

Can anyone help me please? or at least point me in the right direction?