The formation of frost on propane regulators is quite common and usually nothing to be concerned about, provided everything is operating as it should. As propane vapor boiled off the top of the liquid travels through piping to the appliance, it passes through a regulator where its pressure is reduced to safe levels. At this point, it expands and cools, causing the regulator and other metal surfaces to approach the very cold temperature of the vapor within it. This can easily be remedied through simple adjustments to the propane system.
Check to make sure that the propane tank is standing upright and positioned according to the manufacturer's directions. If it is improperly situated with respect to the other elements in the propane system, frigid liquid propane can back up into the regulator as well as downstream appliances.
Avoid overfilling the propane tank when refilling it, as this, too can often result in liquid propane runoff entering the regulator.
Install an Overfill Protection Device, or OPD valve in your tank or cylinder. These valves help prevent overfilling of the tanks and drastically reduce the chance of fluid backup.
Position two or more propane tanks close to each other to create a larger thermal mass, which will be slower to freeze.
Wrap the propane tank or tanks in electrically heated blankets in especially severe cases.
Use propane gas that has been injected with methyl alcohol additive. Propane fuels that have been mixed with this substance are less likely to causing freezing.