halstead ace high repeat lockout?

please help, my halstead ace high keeps locking out. once it fires up it works fine but every morning or evening when i get home from work the boiler is on lockout. sometimes one reset will work but other times can take 30 mins of constant resetting. ive had a couple of people look at the boiler one of which checked the air switch but that was working fine i would greatly appreciate any ideas as to what the problem could be.

colj79
August 2011