how do i fix my worcester boiler?

my Worcester greenstar si junior boiler has always needed the water pressure topping up time to time since installation. my problem started when I forgot to check the pressure and it went to zero, the reset button started flashing I pressed it in on a few occasions but it still did not light. I turned the boiler off at the mains it made no difference other than the reset buttons light goes off when I press it but the blue light below it starts to flash, any ideas please.