Lift up the propane tank and feel its weight compared to a full propane tank if gas isn’t being supplied. After you’ve had a patio heater for a while you should be able to judge the fullness of the tank by the weight. Empty tanks are considerably lighter than full ones. Fill the tank, or replace it with a full tank if it’s empty.
Verify the propane tank is switched on. The tank has a supply valve on the top. It will be marked “Open” and “Close” with arrows pointing in the direction you should turn the valve.
Hold the control knob in at the light position--it’s sometimes marked “Pilot.” Then press the igniter while holding the control knob in. Keep it held until the burner lights. Then move the knob to the run position, usually marked “Low” or High.”
Allow the patio heater to cool and using a pipe cleaner, poke any debris like carbon deposits or insects clear of the burner orifices. Clear the orifices if the flame sputters or burns unevenly. Compressed air can be useful to clean harder-to-reach parts. Make sure the tank is off before attempting this.