I have a T618 treadmill purchased new on Feb 7, 2023. It has developed an electronics issue where the controls often don't work. They still work some times and when they do the treadmill runs and inclines as expected which makes me think that it is an issue with a control circuit board and not the motor. Parts are still available (https://www.fitnessrepairparts.com/m/equipment/Select/33335/Nautilus-Residential/T618-100647?gad_source=1&gad_campaignid= show contact info
&gbraid=0AAAAAD_W5wV_jviH1CZAX7fkW53lhhZI1&gclid=CjwKCAiAt8bIBhBpEiwAzH1w6fE5xlklXe7XY9Z2MkiAop-vdkFr4qnknjUJbU7ymBweJXXxe0flyBoChH8QAvD_BwE). The motor control board is $389 but I don't have the time or experience to do the repair. Can share the receipt. It is technically under warranty but since the line is discontinued I have not had any success so far for getting them to pay for replacement parts.
Partially disassembled but very heavy. Need two strong people. On the street at: