Atwood water heater heating to tepid then shuts off

Mine doesn't have a temp switch as far as I know. The manual says "Electronic ignition: light unit by pushing button inside the coach. Water temperature is non-adjustable."

I'm looking at the wiring diagram and there are a few temperature related parts on it:

-fixed temperature control thermostat
-thermal cut-off

I should be looking at which one of these?

Thank you so much for the quick reply!

Rae