I have a Rheem gas hot water heater near about 12 years old. About a year ago I replaced the igniter. Now at times the vent will come on and the gas won't ignite - if I turn the power switch off wait a few seconds turn back on everything works fine - glow plug works, fire lites, we get hot water. This might work a day or two, then I hear the power vent on and no fire - turn off turn back on works fine. Any answers?