As posted..Suburban WH has an OEM on/off switch for electric in outside compartment.
If you have a On/Off switch inside for electric then outside one has to be ON also for electric to work.
Suburban uses a 1440W electric element.....6.2 gal/hr recovery time
Suburban uses a 12,000 propane burner..... 10+ gal/hr recovery time
Or both electric/propane......16+ gal/hr recovery time
Location of OEM electric on/off switch

IF both electric switches are ON and no heating then element could be bad.
Continuity test with power off ---element under cover behind burner/gas valve
*Test between black wire terminal and white wire terminal.....no continuity then element bad
*Test between white wire terminal and element flange....continuity then element is shorted
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IF THOR uses an Atwood Brand WH
Propane works....heats OK then ALL common components are good (thermal fuse/t-stat/ECO/circuit board 2A fuse)
That means issue is most likely with electric element being bad
OR
dirty contacts----pull connectors off circuit board and clean edge connector using a pencil eraser. White Wire to connector is from On/Off switch and Yellow wire goes to 'dc relay' that triggers electric power to element
Element is under cover with relay on backside of WH tank