Water heater problem

[Ricohtech]

6 gallon suburban water heater with dsi propane tries to light even with the switch off. Just replaced the electric element and thermostat, works fine on electricity, but my fault light has been coming on this season. I've replaced the control board, no change. If the water gets cold enough, which it usually doesn't since it's been heated by the electric element, it will fire and heat, then shut off. My problem is, I can hear it sparking and trying to light all the time. My electric element had been bad for a season or two before this, and I ran propane only with no problem. The only thing I haven't replaced is the switch panel on the inside, which has the switch for propane for the water heater and the fault light. Any ideas?