Richard
Some of what I suggest may have been mentioned, but this is my input.
We have an 08 Beaver Marquis, so I'm assuming you have three A/C/Heat pumps on the roof and One master thermostat with three temp sensors throughout living area of coach and one temp sensor in water tank bay.
Heat pumps should have nothing to do with floor registers.
Thermostate: There may be or should be four zones; three zones for living quarters need to be on "furnace", the forth zone "furnace" is for our rear bath and water bay but the water heat exchanger only operates through the selectable temp range that is in the bay.
If you do not have rear bath, you may just have three zones.
I suggest to make sure your thermostat control has all Three zones set on "furnace" and temperature selected above ambient temperature. If all fans come on throughout the coach, then your registers that do not provide any heat would indicate a circulation problem caused more likely by the zone circulating pump on the aqua hot and lets assume your aqua hot is providing the heated coolant either by electric elements or diesel burner.
In this mode, you need to access the aqua hot by taking off the hood to listen or feel if the appropriate circulating pump is operating. If it is not operating, try tapping on it which at times is effective.
In my opinion this is step one, and then proceed beyond this, if there is no resolution to the problem, as others have suggested.
Good Luck