I am suspecting board is bad,
Here is how it works:
On call for heat board checks to make sure pressure switch is "open".If not nothing else will happen and board will give an error indicating PS closed.
If pressure switch is open, board sends 120v to inducer.
Inducer pulls a vacuum on switch closing it.
Once board senses pressure switch is closed, it signals igniter. Once igniter is hot or sparks, depending type, board sends 24v to gas valve and it opens allowing burners to light. Then the flame sensor verifies flame lit and allows burners to keep burning and energizes main blower.
If any of those components fail to do there job, burners shut down, inducer and blower keep running and we get an error code..
But at no time during the cycle should inducer ever stop until thermostat has satisfied.