New to forum did a search and not sure if I found right answer to my question. First off heater is 1997 when pool was built all original, I just replaced the 2 stage regulator because I had not used the heater in about 3 years and had to repair a under ground line that was damaged when running new power to house. Now when I go to start heater it will light say on for about 1/2 second and shut off and go through the start cycle again, I have read about cleaning the flame sencer just not sure how to get to it? Thanks Mark