WH BRAND AND MODEL WILL HELP, but generically, most common problem is a failure to light when first turned on, and this is caused by AIR IN THE PIPING vs GAS. Best practice is turn on gas valve at tank slowly, FULLY, so that hose rupture safety does not trip, then light stovetop to bleed air out of piping. After bleeding air at stovetop, refrig and WH generally will still require 2-3 RESET attempt, in order to bleed remaining air. Systems should be reliable after that until a hose removed to change a tank, usually trailers? Good Luck. IF model has no pilot, best relabel to FAULT.