Hi. I have a Rheem Power Vent hot water heater, model PVW50-36FV, that won't turn on. The far right and left LED lights indicate the FV sensor detected the presence of flammable vapors. The unit is shut down and in lockout mode. How do I unlock this baby? Checked the sensor and it's within normal operating range so I don't think it's a problem with the sensor. Any help would be appreciated.