Ritetemp Vent Free propane fireplace heater?

I have a 30,000 BTU unit that works great as long as I do not use the blower. Very soon after turning the blower on the entire unit shuts off. I have ensured that the air space around the unit is more than adequate and that the room size is sufficient. This is a 20 foot square room. The unit is in one of the corners with plenty of space around it for adequate ventilation. After reading the manual I believe the ODS unit may be bad, however, I am unable to locate this part for my heater which is model RTN300TQ. Based on the above, what is your opinion of what is wrong and where can I locate replacement parts for this unit. Thanks