2 queries regarding my Glow worm 30ci?

Recently have had 2.9 flashing in window have bled the rads which dropped the pressure down to 1.2 but it only happens again once heating kicks in again.
Also for as long as i remember if heating is off and we use the shower upstairs the red light flashes showing F9 once we switch the boiler on and off it works fine if the heating is on it also works fine B.Gas have pratically re built the boiler apart from the matrix board any suggestions !!!!!!!!