Brand: State Select gas water heater 40 gallon,
Model # PR640XCVIT & Serial # F06A000549

The water heater locks, and doesn't heat the water.

UNIT IS LOCKING (not heating water)
**lights A & B turn on...(which means system is lockout) -
there are 4 solutions on the trouble shooting-
1- gas is off or too low to operate
2- hot surface igniter not positioned correctly
3- low voltage to the water heater
4- electric polarity to unit is incorrect

The unit have been working over five (5) years, never had issues till know. I have to disconnect and reconnect the water heater, which heats the water for a couple of hours, then it locks again (no hot water); have been doing this since December.