Generac 20kW — Before starting, complete the following:

For the Generac 20kW.

Procedure

1. Set the generator’s main circuit breaker to its OFF (or OPEN) position.
2. Set the generator's AUTO/OFF/MANUAL switch to the OFF position.
3. Turn OFF all breakers on the load center of the transfer box (T1 and T2).
4. Turn OFF all loads connected to the transfer switch terminals T1 and T2.
5. Check the engine crankcase oil level and, if necessary, fill to the dipstick FULL mark with the recommended oil. Do not fill above the FULL mark.
6. Check the fuel supply. Gaseous fuel lines must have been properly purged and leak tested in accordance with applicable fuel-gas codes. All fuel shutoff valves in the fuel supply lines must be open. During initial start up only, the generator may exceed the normal number of start attempts and experience an “over crank” fault (See the "Overcrank" section). This is due to accumulated air in the fuel system during installation. Reset the control board and restart up to two more times, if necessary. If unit fails to start, contact the local dealer for assistance. n Never operate the engine with the oil level below the “Add” mark on the dipstick. Doing this could damage the engine.
2.3 CHECK TRANSFER SWITCH OPERATION Refer to the "Manual Transfer Operation" section, of the owner’s manual for procedures.

Source: manual:9f84685f-0bec-42e0-a4e9-5c2c50b4b67b.pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.