probably dont have one they are made by amercian water company with multi design/configurations if only one thermostat then also only one element the upper is also the electric connections
The error code 13 indicates that the PTG2-42PVN is not getting enough air or the vent termination is blocked. Check both the intake and exhaust termination for blockages and remove any debris. Make sure that you have good air flow in the room (no other vents should be blocked). Clean any other blocked vents. If you use a fireplace or space heater in that area, open a window or vent to increase the oxygen levels in the room. If other appliances are used in the area, make sure that they aren't affecting the ventilation and oxygen levels in the area. If you bring in air to the water heater from the outside, make sure that other appliances aren't exhausted to that area.
ManualsLib has the manual for the PTG2-42PVN: https://www.manualslib.com/products/Rheem-Ptg2-42-Pvn-Pvp-330558.html . The error codes and solutions are listed on page 33: https://www.manualslib.com/manual/140606/Rheem-Ph-16-Fisn-Fisp.html?page=33#manual .
I hope this helps.
Cindy Wells
You only need the thermocouple replacing. It is the safety valve that won't let the main burner light unless the pilot is fully lit. As it is gas, you should have a gas certified technician replace it.