My heater has an electronic ignition (called "IID"?) and has stopped lighting the heater.
The igniter is sparking just fine; you can clearly hear it, and I pulled it and visually confirmed the arcing.
The heater HAS lit once or twice this season, but does not light regularly. I pulled the ignition module out and blew through the tube that takes gas from the thermostat to the pilot site; it does not seem to be clogged, but I can't say for sure how much gas gets through; I probably put more force to blowing through it than the natural gas flow does.
The trouble shooting guide says to check that all manual gas valves are open, supply tubing and pressures are good, and that the pilot burner orifice is not blocked. Then to check for 24 Vac across PV-MV/PV terminals on module. If voltage is ok, replace gas control, if not replace module. I have no idea what all that means.