Jim, if you have the Suburban water heater, here is how it is supposed to work. This doesn't apply to a tankless heater, so if that's what you have you can ignore the rest.
When you turn on the inside switch to turn on the Direct Spark Ignitor (DSI), the Reset light (sometimes also labeled as a fault or flt light) initially comes on until the DSI completes the lighting of the propane.
Once the propane ignites, then the light goes off.
However, if the propane fails to ignite, the light stays on to alert you to a problem. Depending on which model suburban water heater you have, then the DSI can go thru two more automatic ignition cycles trying to light the propane. If the propane lights during the second or third attempt, then the light goes off.
However, if the propane fails to light after the third series/attempt, then the whole process goes into lockout mode. The propane valve closes and the DSI will not attempt again to light the propane.
You have to reset the lockout, but turning off the DSI switch inside your coach for a few seconds, then turn it back on. The process begins anew. Three tries to ignite.
If it's not lighting, then you have a problem somewhere. You could have spiders webs in your flue, a faulty gas valve, faulty regulator on your cylinders, etc. You can also have the gap misaligned on your ignitor.
Hold on and I will get you some links.
This FAQ may help also:
Suburban's electric switch and much more