i have a raypak 2100 digital multivolt heater, unit has worked great for almost ten years but has recently started acting up

the unit temp settings climbs to 104 on its own. the switches were not working well so i replaced them but the same problem remains

its like the temp up key is stuck, i turn it down and then watch the numbers climb right back up to limit.

i have been turning it on and off manually to regulate

how do i fix this???