Dometic RM2453 uses DSI direct spark ignition not a standing pilot or 2-stage burner. Burner ignites on demand when thermostat calls for cooling. Single stage operation runs full on or off.
Girard II tankless requires different wiring than DSI tank heater. Run new 10 gauge 12V power with 30A fuse. Do not reuse old DSI harness. Follow Girard diagram exactly for proper operation.
Everything you need to know about RV plumbing systems from fresh water supply to waste management.