This might happen due to corrosion to the orifice and you don t have any choice apart from replacing it with a new one.
Propane wall mount heater shuts of after 30 sec.
If heater shuts off do not relight until you have provided fresh outside air.
If heater keeps shutting off have it serviced.
Gas valve are allowed 30seconds to fall out.
Also there may be a pilot adjustment valve on your gas valve.
Step 2 close the empty propane tank if it is small enough to remove by turning the handle counterclockwise as far as it will go.
If heater keeps shutting off see troubleshooting pages 22 through 25.
How to troubleshoot gas wall heaters.
There could a fault in the gas valve s main burner solenoid causing it to draw excessive power and starving the pilot flame solenoid.
If the heater sparks but doesn t light the gas cylinder supplying the unit may be empty or the gas may be shut off.
Turn the control from the on position all the way over to the off position.
The third reason of why your propane heater keeps shutting off can be a blocked up gas valve orifice.
If you re sure the unit has gas clean the aperture of the gas valve with a needle.
If so replace the entire valve.
Another reason of such blockage is the presence of air in the gas line.