~10 year old furnace started intermittent lock up with error code 31.
Careful investigation revealed intermittent inducer motor. It starts
but stops running or it won't start when heat is called for.
Took the control board out(HK42FZ004) and went through it. The problem
found was cracked solder joint on two high Wattage resistors R34 and R33
(both 330 Ohms) had cracked solder joints on the PCB due to heat(?).
Reinforced the joints with silver solder. Now furnace is behaving normal
again. Google search showed it is known problem mentioned in service
bulletin. Going price for replacement board is ~200.00.
Hope this may be of some help for someone who has same furnace type.
(Carrier, Bryant, Payne brand uses same board I believe).