Hi Jfarina56,
1st off, are you sure the water heater is running on propane rather than electric?
Even if it is, you may have partial flow of propane; enough for the water heater but not for the furnace. Try turning off both propane tanks - wait 10 seconds - re-open each valve verrrrrry slooowwly. There's an overflow protection device in the tank that can deploy if opened fast.