Red light no longer flashes HKC alarm ?

I had my HKC alarm serviced the other day
since then the red light no longer flashes
When alarm is part set when going to bed at
Night. I called the engineer who said he didn't
Know why. I was surprised he didn't know and he
Didn't offer to come back and look at it . I'm not very
Happy about that as I paid for a service and now
Something that was working perfectly before the service no longer does and he had no idea why this would happen being an engineer I thouht he would have some idea. Can anyone tell me why and if I can fix it myself.HKC Alarm EN50131

Patricia
December 2015