Clothes are too hot
First, my dryer only heats on normal mode. Then the timer gets stuck at 7 minutes left. And, if I do not check the clothes regularly, the clothes get too hot. Why is this happening.
Obviously the timer is malfunctioning. Replace it.
"What @mayer is saying is true, it is likely the timer.
First, I would run the diagnostic. Use the first page in this manual to run the diagnostics. On page 3, it says the cause of these errors. Also on page 3, it covers troubleshooting. Look through that.
Once you've done both things, report the results. If 8:88 is displayed, the damage must be entirely physical. In that case, replace the timer and/or front panel.
Hope this helps!"