As stated above first guess would be air in the lines. Also as stated does the stove work? After verifying the stove works start with the easy stuff like cleaning the flue and burner area. If accessible try lighting by hand. Try to observe the pilot light when someone turns on the gas side. Does the pilot light light then go out after a minute or two? If this is happening then the thermocouple is either not adjusted correctly or is bad. Good luck and be sure and check back to let us know how you made out.