My 5 year old Rheem gas pool heater needs repair. I've had someone come look at it and he replaced the thermostat which had corrosion on it, but basically told me I should replace the heater. He only took the front panel off and seemed hesitant to get too deeply into it. The problem is that it lights and starts heating, but shuts off after about ten minutes. Then I have to shut down the power and restart it...and it does it all over again. Once in a while it will keep running until it gets to the set temperature. I am hesitant to call someone else and go through the cost of another round of servce calls, but I just don't believe I need to replace the heater. How do I find a knowledgeable repair person? I found the first person through Servicemaster.