Lpg boiler?

Ok here is a good one that 2 of my local LPG registered HEATING ENGINEERS couldn't find....MORCO FEB-24ED has power, fan working and showing no fault codes.1 said it was the High limit stat, got it working and told me to order new HLS. Boiler stopped working a few hours later with no fault codes showing . Replaced HLS and did NOT work, engineer ignored my texts and calls!!!! 2nd registered LPG heating engineer came diagnosed PCB FAILURE but got it going, great, then stopped working a hour later, so ordered a New PCB, FITTED AND WORKING, PERFECT, three days later back to a non working boiler showing no fault codes... once again heating engineer ignoring my texts and calls, what is wrong with these people, can someone explain WHY......PLEASE.