I have a RUUD furance and the blower won't shut off. Only way to stop this is to shut the power down. Checked thermostat seems to be working fine. Have any idea?

First idea is to tell us more on what you have, model number how old is furnace ,does it have a circuit board,, is it giving a code(blinking light)if it has a circuit board have you checked for a low voltage fuse in the board

Don't really know its about 10 years old according to the old owner. Don't have a circuit board. Tried to run the furance and it would lite and go out then relite and come on. Then that quit and only two of the three flames came on so I shut it down. And now the blower runs all the time. Turned the power off for two hours and it still runs. Tried to let it run to see if it would quit and it ran for over an hour so turned power off to it. It's a Ruud Silhouette II model # RCBA 2457 GG17
Thanks for any help