I have an AO Smith FPS 50 226 Powershot gas water heater. When there is a demand for hot water, everything starts up normally, but the burner goes out (can hear the solenoid click shutting it down) before the water is up to temp (the blower continues to run and the pilot is lit). While the blower is running, the burner may refire at some point, but then it shuts down again. If I reset it using the on/off switch on the blower, it will refire and continue to burn until it shuts off properly, though not always the first time. I've run some of the tests outlined by the tech manual, but it doesn't seem that this condition fits the ones covered. The blower, power cable (tested for 120 at both and got it), and gas valve solenoid are all fine (replaced the latter to no effect). The wire harness that connects the power cable to the gas pressure valve and solenoid is not showing 120 volts (in fact it shows 0) to the solenoid (according to the manual this could indicate that the harness needs replacement), but continuity is good in all 4 wires (no shorts). Haven't tested the gas valve for pressure yet, nor have I tested the gas pressure switch (though the conditions according to the manual don't point to this being a problem, and I'm not sure how to do that specifically even if it did). I know the water heater is old (about 12 years), but I'm not in a position to replace at the moment. Could it still be the harness, the gas pressure switch, or is there something else I should be looking for?