Blower works, filter is clean. Hot Surface Ignitor glows, burners ignite for 15 seconds, then cuts out. This cycle happens for (3) times. Fault code then blinks (7) times. According to book it means one of (3) things: a) low gas pressure (however my other furnace works fine), b) faulty gas valve, or c) burner problem. Does anyone have an idea of which one of these three it could be?
hawkmjb

Just for the heck of it clean the flame sensor. It is cheap to do and if that is not the problem you have that problem out of the way.

https://www.askmehelpdesk.com/heatin...ay-406739.html

Those are feasible causes, but I am not sure what book you are referring to. If you are referring to the Manual for the System board/controller then that's pretty definitive. If not contact the board manufacturer and see if they have any other ideas. For instance, White Rodgers has some nice flow charts that will pinpoint all the possibilities and even give insight into the boards inner workings.