Hydroflame is a great furnace when PROPERLY maintained. I had two of them in my prior 93 Pace Arrow Diesel. RV furnaces have no filters so they tend to suck anything and everything thru them.
I ended up installing burner that was rusted out preventing it from properly igniting. Also cleaned the squirrel cage blower, replace the electrode and sail switch. Fired up first time, every time. Do it right the first time.
Check out this site for parts, prices. https://pdxrvwholesale.com/
They have tune up kits as well. Do the same for your hot water heater.