I have an inground pool with a Hayward light niche. I replaced the burned out bulb and now the light stays on for about 20 minutes, and then shuts off. A few minutes later it comes back on by itself only to stay on for about 15 minutes. Apparently it is heating up and the thermal sensor is tripping. It never used to do this before. Does this mean the fixture is bad?? Not sure how to proceed....