I have a problem with the heat. I replaced the circuit board & pressure switch. It still flashes 3 times saying pressure switch. Heat does not come on

Clear the pressure tube of debris or obstructions.

Inducer motor does not even come on. Soon as it calls for heat, it blinks 3 times for pressure switch. No voltage to inducer motor.

I think the inducer motor is the first step once the thermostat calls for heat. Check the sequence of operations in the sticky at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html

Check the connection from the board to the inducer motor. Were there jumpers on the old board? In set up, the installer selects different windings for the motor to match its speed to the vent. You want to make sure the board is powering the terminals your inducer is connected to.