There is also a layman's method to do a crude regulator test.
Light a burner on the stove and turn it on high. Observe the height of the flame.
With that burner lit, turn on either the furnace or the hot water heater.
The flame on the stove burner should dip only momentarily and then return to the original height. If it does not, suspect one of the regulators.
As Herk mentioned, in many of the new RVs with propane tanks on both sides there is an additional first stage regulator (sometimes red in color) on the propane tank opposite the tank with the change over valve installed.
You can narrow it down to that first stage regulator by running the test using the each of the tanks, and if the flame does NOT stay smaller when the tank with the change over valve is used, suspect the first stage regulator on the far tank.
Also, this link is a must read for any propane related issues, thanks to Herk.
Red Propane Regulator
2013 Rockwood 8289WS
Mods: Central Vac, PI EMS-HW50C, 2025RV, (2) SCS225 Trojans, PD9260, Awning Remotes & LED Lights, Eliminators, External Water Filter,, Intellijacks
2008 RAM 3500 Cab&Chassis Hauler Bed, B&W Companion Hitch
All My Modifications are at this link: