Samantha - call an engineer - allow him to change only one thing at your expense - be firm - tell him up-front that you want diagnosis and not guesses - otherwise he might change things on spec and have you pay for his incorrect guesses. Remember that it's you that's paying. Ask - "why are you changing that - and what if it doesn't cure the problem?"
The problem you have may be one of several things - not two or three...
Fan not working as it should
Pressure switch failing to detect fan operating
Pilot gas valve not opening
No spark to light pilot flame
Pilot flame sensor not detecting heat
Weak pilot flame
Main gas valve not opening
Control electronics defective.
Good Luck...
May 2016