Boiler still flashing red and green after repressurising system to 1.5 bar?

Hello....
I have an Alpha SY24 boiler...this evening i put the hot water on. Boiler fired up ok. However at some point it switched off and started flashing red and green intermittently. The pressure gauge was too low, so i have repressurised - pressure now sitting correctly at 1.5 bars. I have moved the selector switch into the reset position, but to no avail, boiler still not firing up.

Any suggestions will be very gratefully received

Jemima.