Ok, I am making a few assumptions here:
1) Pump and/or city water is on/connected flowing
2) The water heater is on and LP valves are on and you bled the line and stove lights
2a) If heater is electric, verify it's on, heating and no tripped breaker.
3) Water heater is lit and actively heats water.
From there, I would look for the three valves that bypass. Supply and output valves turned counter clockwise, center bypass valve turned counter clockwise disabling the bypass.
By having valves turned as suggested, water pressure automagically fills water heater.