quad 1200cb will not shut down

i have two quad 1200 cb one is a year old the other one is nine years old. The nine year old one is in my basement i noticed that almost all the pellets were in the hopper and ash pan without the thermosat being turned on. I cleaned everything up and she stated right up.WHEN i went to lower the themosat she would not shut down.I disconected the thermosat and it still would not shut down. I empted all the pellets and it shut down. What i did notice is that the augger keeps running it only gos off by unplugging the stove.Help does any one know if this is a control box issue. Easy to replace but expensive.I want to be sure before i order it Thanks