Error A108 means the heating source defaults to elements due to condensate drain blockage. The following steps can help you check the issue.
Remove the top cover from the tank
Visually inspect to ensure condensate line is clear and there is not excessive condensate in the condensate pan
If water is present, locate the blockage and unlock it.
Ask the customer where the condensate is being routed
If the pan is dry and no blockage is present, replace the condensate sensor.
Also, this is often caused by a frozen condensate line during the winter.  So, depending on how the condensate line was installed and if it was uninsulated that could be a potential cause.  If you are able to test that water runs through the condensate line clearly then that could point to needing to replace a condensate sensor.
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.