Have HVAC Questions? Ask an HVAC Expert for Answers
Do you have a multi meter?
Of your gas valve you have a purple wire and a blue wire. The purple wire runs through a series of roll out manual reset switches. Follow this purple wire from gas valve to each limit and press the small button in the middle of each switch to make sure none of them are tripped.
If none of them solve the problem then you would need a multi meter to test at gas valve and see if you are getting 24v about 10-20 seconds after igniter lights up. If no voltage then one of these limits is indeed tripped or you have a bad control board. If you are getting voltage then you either have no gas supply or your gas valve is bad and not opening.