There should be a Suburban Water Heater Diagnosis Guide in the Files section of the forum. Go to
https://www.montanaowners.com/forums...hp?do=cat&id=3 and look for "
Water Heater Troubleshooting - Suburban " and "
Suburban Water Heater Service & Training Manual" (or just click on the manual names here - I didn't realize copying the names also copied the link to them)
Often spark/no gas is due to the gas valve. It has two solenoids which open the flow of gas. They can fail and are easily replaced. Here is one of many posts on these doodads.
https://www.montanaowners.com/forums...1212803&nojs=1
It is easy to test the solenoids. Also do a Search on " water heater solenoid".