INFRARED HEATER WILL NOT STAY ON. PILOT KEEPS GOING OUT AND UNIT

WHEN I TURN THE PILOT ON AND THEN GO TO TURN THE GAS DIAL AROUND TO TURN THE GRATES ON, THE PILOT WILL SHUT OFF. WE HAVE TO BLOW AND GET THE PIECE BESIDE THE PILOT HOT AND TILT THE HEATER TO KEEP IT ON AND SOMETIMES THAT WANT WORK. I HAVE 2 RINNAI INFRARED HEATERS HEATERS. ONE IS A 3 GRATE AND THE OTHER IS A 4 GRATE AND BOTH ARE DOING THE SAME THING. MY FATER- N -LAWS ARE DOING THE SAME ALSO. HOW CAN I FIX THIS PROBLEM? MY
UNITS ARE PROPANE.