I have a gmp 075-3 I havea control board icm 280 and b1809913.The 280 everything comes on except the blower motor.the b1809913 everything comes on except the flame and the led blinks 4 times with the other board icm 280 solid led no blower motor go figure that out and there both new.anybody got an answer to this puzzel.

Have you tried running the unit with the thermostat bypassed? Jumper "R" and "W" circuits together, either at the furnace or at the thermostat location. Post results.