Error A008 refers to the Dry fire protection and usually means that there is no sufficient water in the storage tank and the heater was disabled. The following steps can help you check the issue.
Fill the storage tank with water.
Purge all air from the storage tank by running a hot water faucet (This is generally an installation issue and indicates there is air in the tank.) If the unit is still displaying the A008, the air is still present and should be purged again. Any issues with the board or sensors would exhibit a different alarm code.
Zwell is dedicated to getting homes closer to net zero through the installation of new energy-efficient hybrid water heaters. We are not currently equipped to do service or repair visits but we want to be as helpful as possible. Feel free to reach out to us here or for more information, you can contact the Rheem Hybrid Technical Services Department at 800-995-0982.