Originally Posted by TCNashville
You might want to consider using a water pressure regulator at the spigot before turning on the water to your unit. Don't forget to open a hot side tap as the water will fill the water heater first releasing the air trapped in the heater.
I looked at my manual and this is what it states, is this what you are referring to?
"The water heater (if so equipped) will fill first, followed by the supply lines and faucets. Water heater bypass valves (if so equipped) A and B must be open to allow water into the water heater, valve C should be closed. Refer to the water Heater bypass section."