ksg5000 wrote:
Not sure about "hissing" but a propane water heater has a large visible flame - go outside and see what the flame looks like. If no flame then - see if you can smell gas. If no flame and you can smell gas then you might need to remove the spark assembly - clean the probes with emery board and make sure they are within correct range for ignition. You just need to remove a screw or two - not hard.
I have a similar problem and I have the SW6P not DSI. I don't smell gas at the hot WH when I try to light my pilot. suggestions? Could air in the line cause this?