Air source heat pump not heating after new cylinder installed

Hello, I’m really hoping someone can help. I moved into a flat a year ago that has air source heat pump instead of a boiler. I had a crack in my indirect water cylinder. Have had it replaced like for like, yet now the air source just is not heating my hot water or radiators AT ALL! Everything is connected and working as far as we can tell and we have been running it in case it’s air in the system. But after a week, still no sign of it heating the system at all. I have been using the immersion side so I have some hot water, and when the heat pump is on for the heating side it seems to be taking all the heat out of the tank. Yet it was all working before when there was a crack in the cylinder.