Heater won't refire after it warms up. My heater is plugged into a thermostat that I have set at

Question

My heater is plugged into a thermostat that I have set at around 65 degrees my garage is appox. 30 degrees. When the heater is cold and I first plug it in it runs good after the thermostat is satisfied and the heater shuts off the temp. of course drops to where the thermostat again fires up the heater ( which is still warn ) now the heater will run blowing out lots of smoke but not fire up for anywhere between 10 secs. to the point where I have to manually unplug it. The next day or when the heater has totally cooled its initial start is fine then the problem starts all over. Any ideas ? The heater is a Ready Heater Pro 150,000 btu Thanks, Mike