No hot water supply/flow?

Hi,

Have replaced a mixer shower, it has a feed from cold water tank and hot water Emersion tank.

Turn off all water values before, and had no problems with water pressure etc.

Once unit was swapped, and water turned on again cold water supply to all taps in the house if fine. Hot water hardly any flow, then stops (sometimes splattering occurs, before stopping). This is for all taps in the house, and shower.

Sounds like hot water Emersion tank is not filling up to replace lost water. Any ideas more than welcome.

Mixer shower model no Showerforce SF1000-XM

Kind Regards
Daniel