Valliant EcoPro: I can't increase the pressure?

This morning the pressure level in my shower was very low. I tried to increase the pressure in my boiler to see if that helped (it was at 1.4). When I went to turn the 2nd tap to increase pressure - as usual - nothing happened and a few drops of water came out. I have never had any problem increasing the pressure before and I don't know what to do. There is no error message.