Your boiler is currently running a self-clearing cycle to remove air from the system, which happens automatically after you have topped up the water pressure.

Filling the product: The prioritising diverter valve is moved to the mid-position. The burner and pump are switched off (to fill or drain the product). If the pressure is lower than 0.05 MPa (0.5 bar) and then is above 0.07 MPa (0.7 bar) for longer than 15 seconds, the automatic purging function is activated. The function is activated for 15 minutes.