Carrier Furnace 58MVP080F17114 Displays Trouble Code #42 Was installed in 2003 has run trouble free since install ; Will operate randomly on second stage will sometimes operate on first stage for several hours then go into lockout mode and shuts off gas supply . Sometimes I must cut power supply for 5min to restart. Have checked air intake and exhaust outside;no restrictions. Do you have any suggestions or further checks I can perform to replace defective part or correct the problem

thanks