About a month ago, the water went cold. The blower was on, but neither the pilot nor the burner were lit. I unplugged the unit, then replugged. The blower and the pilot came on, and then the burner came on. I let the water heat up until the burner turned off. Then I ran hot water until the burner reignited. I cycled it a couple of times with all working okay.
The problem resurfaced yesterday with the same symptoms. Once again, cycling power fixed the problem.
Since cycling power fixes the problem, it seems the problem may actually be at shut down. Would a stuck thermostat cause an overheat that does not allow the unit to come back on? Or does it seem like a valve assembly problem?
I suspect the pilot burner is the main problem and is probably not large enough or clean enough to prevent it from being sucked back off the pilot burner jet, this would happen when the main burner shut down upon reaching the preset water temeperature and is not that uncommon and is easily fixed with a little care and attemtion.