I HAVE A 30,000BTU PROPANE HEATER (REDDY). i USE IT IN MY WORKSHOP AND IT PERFORMED FLAWLESSLY LAST WINTER. I HOOKED IT UP TODAY AND IT WOULD START BUT WHEN AFTER 30 SECONDS, I LET THE PRIMER OUT IT STOPS.

There is a thermal couple (sensor) that senses the temp., and if it is defective it will shut down. Replace the thermal sensor and it will work fine.

Always start by checking the pump pressure, first. Compare the air pump pressure to specs written on the heater. So much time can be gained in troubleshooting by using pump pressure as a starting point. Pressure loss can lead you to rotor failure, air leaks, broken parts, leaky hoses, or, through good intentions, if someone has attempted to adjust the pressure and actually done more harm than good. As little as 1/2 psi reduction in pressure can give the symptoms described. Once the pressure is correct and the problem persists, move on to diagnosing the nozzle, fuel, and fuel delivery.
Fuel delivery is directly related to the air pump pressure. Just like the doctor checks your blood pressure (blood flow) you need to check the heater's air pressure (fuel flow). Air travels from the pump to the nozzle. At the nozzle adapter, fuel is sucked from the tank. Too little pressure means reduced fuel flow.