Your boiler is currently running an automatic filling or air-clearing process, which usually happens after the system pressure has been adjusted.

Filling the product: The prioritising diverter valve moves to the mid-position. The burner and pumps switch off (to fill or drain the product). If the pressure is lower than 0.03 MPa (0.3 bar) and then is above 0.05 MPa (0.5 bar) for longer than 15 seconds, the automatic purging function is activated. The function is active for 15 minutes.