Reading productive data from flow heaters

Hi, I’m looking for a way to record the data (power consumption, water consumption, etc.) transmitted by an instantaneous water heater (here: Vaillant VED E 18/7) via BT to a remote display in HA; a Shelly Plus1Mini with an activated BT extender would be nearby as a gateway.
But how can I carry out the data retrieval, which is initiated by default from the remote display, from HA … and how can I connect the Vaillant BT transmitter to HA (Shelly?)?
Thanks for any advice or reference to appropriate solutions.