Hi Judy, I just flushed ours, necessary annual chore!
The two things you note should not be related - flushing and lighting the appliances. Have you checked to be sure you have power to the rig ... shore line or battery? If you are sure you have gas in the lines, the likely culprit is no power to the igniter circuit.
Be sure the gas lines are purged of air ... I usually light a stove burner when I first turn on the gas to enable it to quickly come up to pressure, but do that with some ventilation. It often takes several attempts before gas is in the line from the tanks. Once a stove burner lights, there should be enough gas for the other appliances to light up.
Be sure on your water heater that you have closed the bypass valve in the WH compartment and opened the hot and cold valves at the WH (... not sure where that is in your TT, but is accessible from inside normally) and then be sure the heater is full before lighting.
Smart to start the furnace and WH ... don't forget to check the fridge to see that it also lights up for gas operation!
Good luck and I'm sure you'll get some more suggestions here!
Fred n' Jeri
2012 FF X-214WSD
2010 RAM 1500 Crew Cab 4x4, 5.7 Hemi MDS, Huskey 1200lb trunnion WD, Prodigy Brake
Prion Seayak Kayaks