The first possible cause is the use of a new propane tank that has been improperly filled. New tanks must first be purged of air before being filled with propane. Purging requires that the tank be filled with a small quantity of propane then emptied. The propane being heavier than air will force all the air out of the tank during the emptying and leave only propane vapor in the tank. The tank can then be filled and, when used, the tank will emit only propane vapor. If the tank is not purged, the air in tank will be emitted into the grill first and will either not burn at all or burn with a very low flame. It can take over an hour to vent the air from a non-purged propane tank through a grill's regulator and valve. Always make sure a new propane tank is purged before filling.
The second possible cause is the surge protection device built into the grill's regulator. All Coleman Grills have the surge protection device. This device cuts the flow of fuel to the grill if a sudden increase in propane flow is detected. This is to prevent a large venting of propane if the hose or valve on the grill is damaged. This device is also activated if the burner valves on the grill are in the open position when the valve on the tank is opened. You want to always be sure the burner knobs on the grill are in the off position before shutting off the tank valve when shutting down the grill. Just turning the knobs to the right until they stop may not turn off the burners. Most knobs must be pushed in and turned to the right before they will fully shut off the grill. Always make sure the knobs are in the off position before opening the tank valve when starting the grill. If either one of the knobs are in the open position, the surge protection device will activate and the flow of fuel to the grill will be very low.
The third possible cause is the use of an Overflow Protection Device that is now required on all propane tanks sold in the United States. This device is built into the tank and prevents too much propane from being put into the tank. It involves a float that rises on the liquid propane in the tank and shuts the valve if too much propane is put into the tank. Though this device is primarily used when the tank is being filled, it can also activate if the tank is tipped. Most propane cylinders on grills are stored below the grill body itself on a plate just above the wheels. If the grill is tilted when being moved, the moving liquid propane in the tank can cause the float inside the tank to rise and activate the OPD. This will shut off the flow of propane through the valve.