Heater won't stay lit.

I have a reddy heater RLP35. When I plug it in and turn on the gas, hold in the orifice button and push the striker the unit lights and I hold the orifice button down for a minute or two, but when I let go of the orifice button the flame goes out. I cleaned out the inside of the unit like the manual said. It didn't make any difference. Any suggestions. Thanks in advance for the help. kboyd63389@yahoo.com