If you re sure the unit has gas clean the aperture of the gas valve with a needle.
Propane wall mount heater shuts of after 30 sec.
Also there may be a pilot adjustment valve on your gas valve.
Keep all air openings in front top and bottom of heater free of objects and debris to ensure adequate air for proper combustion.
On wall mount heaters it is usually located on the front of the heater near the floor.
This might happen due to corrosion to the orifice and you don t have any choice apart from replacing it with a new one.
If heater shuts off do not relight until you have provided fresh outside air.
Gas wall heaters whether vented or unvented can supply enough heat to warm a small or medium sized room and they can operate with propane or natural gas.
If heater keeps shutting off see troubleshooting pages 22 through 25.
There could a fault in the gas valve s main burner solenoid causing it to draw excessive power and starving the pilot flame solenoid.
Gas valve are allowed 30seconds to fall out.
How to troubleshoot gas wall heaters.
If so replace the entire valve.
If heater keeps shutting off have it serviced.
The third reason of why your propane heater keeps shutting off can be a blocked up gas valve orifice.
Turn the control from the on position all the way over to the off position.