First steps to debugging a propane device that will not light

1. Do you have propane in the tank(s)?
2. Is the propane valve turned on?
3. If you have more than 1 tank, is the switchover device(if it is manual) switched to the tank with propane in it?
4. Have you lit your stove top to make sure propane is flowing?
5. Retry the non-lighting device.

Still not working?

Do you hear clicking or is it a pilot light(older) device?

If yes on clicking, then you have a direct spark ignition(DSI).  Still sounds like propane not getting to device.  It could be junk(spiders, mud daubers, etc) in the area where the propane would be ignited.  Do you see anything in there, can you smell propane?

If no clicking is it an older fridge, furnace that has a pilot light?

If not an older device and no clicking is your battery fully charged, using a voltmeter what the voltage on your battery, as DSI and control board needs 12v DC, aka battery power to operate correctly.

Water Heater: Go outside, open the door to the back of the water heater, do you see any loose or broken wires?