You may need help with this, but light the pilot (have someone else push the knob in). Before you turn the switch to "on", light a fire starter - cigarrette lighter or BBQ lighter, and hold it right by the pilot light (you now have 2 flames that become one. NOW have the second person turn the know to the on position. The flame should ignite in the water heater. The real test will be when the water heater reaches temperature, will the pilot stay lit?
I had to do a variation of this process on my Dutchmen. But found the knob had a sweet spot where, when pushed, and then turned, it allowed gas to seep for the flame and the pilot.
I think what's happening, when you flip the knob, there is one spot when the pilot light actually turns off (killing the flame), and then the heater won't ignite (no flame). It's such a minuscule spot on the switch, it's hard to catch it.
Try it. If this does not work, maybe the thermocoupler needs replaced.
Good luck!
