The most likely reason is a faulty AC adapter forcing the board to stay in the "boot loop." The "C424"(or similar) identifies the program installed on the valve and is only displayed briefly during the initial board loading. If the power supply does not supply the proper amount of power to the board consistently, it can trick the board into thinking it keeps getting turned on.
The first step is replacing the AC adapter. In unlikely chance, if that doesn't fix the issue, a replacement board will be required.