I have a byrant furnace that went out. Checked the igniter put everything back together and it worked fine for about four hours. Now when the thermostat calls for heat the blower motor comes on but the draft motor will not come on or the thermocouple. The induced draft motor is only getting three volts from the control board. I feel that it might be the control board, but is there anything else it could be?

3 volts at the board for the inducer will not get it.

gonna need 120v for inducer, but i am concerned about you working on this yourself when you mention a thermocouple on a draft induced furnace. Can you please explain what you are calling the thermocouple. I would start by jumping r and w at the board, see if inducer comes on. If it does, you have either bad thermostat or thermostat wiring. Please let me know what you find.

What's the model #?

Check for a open limit(roll out,high temp,blower, etc). If you have a open limit the blower will run all the time and nothing on the heat side of the furnace will work.