I have a Goodman GPM furnace. It works intermittently. I checked the breaker, thermostat, Control board and surface igniter. All appears well on start up sequence ; blower runs and igniter heats up and then turns off as no gas comes out. Control board codes says OK and I also turned to fan switch on and it works just no heat. Can anybody recommend what to do next. The house and unit is 10 years old and I have had no problems until now. Thanks

Do you, at any point during the ignition process, get 24 volts AC to the gas valve?

It sounds like you have a bad control board. If you had a flame proving fault-(no flame after 24v going to gas valve) or a pressure switch or limit switch open it would give the fault code on the control board. To rule out the thermostat you will need to jumper R to W at the thermostat connections and see if it works. A weak or bad heat anticipator on the thermostat will give the same symptom.