Atwood 6 gallon water heater -- gas valve issues
There is no pressure sensing device in the water heater. Releasing the pressure only results in reducing the head of air. A head of air is necessary to prevent over pressurizing the system.
Think of what would happen if you locked the lid of your tea kettle to prevent it from releasing steam. While the water heater would not get to that extreme it will build pressure unnecessarily.
The proper way to establish the correct air head is to drain some water from the water heater. Then close all valves in the water system and turn on the pump or city water. Then open a sink hot water valve and let the water run until all air is out of the lines.
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