and Welcome to the Forum!
What "oil reservoir" are you referring to?
Start finding the identification tags for all the appliances and systems, Furnace, fridge, water heater, etc. You should be able to find those service manuals online. This web site link below should get you started. If you find the furnace manual, it will help you troubleshoot the no-start. Manual starting is not normally possible due to the safety interlocks in place so you don't blow yourself up.
Service Documents and Manuals
Depending on what chassis you have under that coach you can probably find an Owner's or Service chassis manual online too.
Best of Luck!