If the only problem is the water heater, the water heater could be the problem. Did you adjust the pressure on the water heater and furnace. There should be a nipple you hook a tube to and a meter will read the pressure. I can not remember what it is called, but I know it was done on my propane furnace. From what I remember it comes into play when when you run more than one item.

[s][/s][quote=white17]Try what MJM suggested and see if it makes a difference. Be careful though because you could get a surge of propane to the appliance. There have been some bad accidents up here from folks heating their regulator. Sounds like condensation in the line or in the regulators. You COULD shut off the gas and take the regulators in the house and heat them to dry them out . Replace and see it that helps.

Usually the only time we see problems is at minus 40 or if the tank is low on fuel[/quote Ute
The last part of White 17 is the correct one. I managed a branch office for a propane destributor, tank sets, plumbing, appliance conversion the works.
More than likely condensation in regulator or simply a bad one. They do go bad on occasion. Close main valve on tank, remove regulator take inside and heat with a hair dryer or similar till warm to the touch tap the output side on a paper towel to check for condensation, tap diaphram body with hammer handle reinstall with body of regulator horizontal , purge line and Check all connections for leaks. Restart appliances and check for proper function. If problem persists have your supplier inject some dryer into the tank, methanol. This should have been done at time of installation.
Unfortunate timing hope you get it going ok
Propane has a vapor pressure of -44* if the ambient temperature is warmer than that you should have gas.
Butane is around -8* if I remember correctly

... I can’t help all I have is a little 150 gal for a heater... but I hope you get it figured out cause that sounds like a real propane in the a.....