If you have 110V you are still low as the optimum today is 120V and most line monitors will turn power off at 108V which is the design low limit for most appliances.
If you do not have one, here is a copy of the
Suburban Service Manual that covers the NT-34SP model. If the ignitor isn't sparking and the sail switch is not closing it could be some sort of air restriction preventing enough air movement or it could also be low voltage to the blower motor will cause it to run slower than normal and could cause the sail switch to not close. To be sure of the voltage you need to check it will an accurate meter while the blower is running and you need to see at least 11V.