Probably the water diverter motor gone on the heater box which may have taken out the triac on the module too.
The switch between top and bottom arms should occur approx every 60secs once the machine is fully up and running.
Check the triacs on the main board. If you find the top or corner blown off one of them then both heater box and module will need replacing ….not the cheapest of repairs !!! 🙁