THERMOSTAT CONTROL ON BOARD WONT WORK

It is hard to say without knowing weather knowing if this is a milivolt or electronic heater. In ether case you can replace parts, just witch parts is the question. A milivolt heater the thermostat will be sold as a unit that screws onto the faceplate and has a temp probe that will snake around to the water header and slip into it. An electronic heater will have a thermister that will also go into the header and ether have wires that plug into it or wires connected to it that plug into the board. This is often the problem with these and are cheap and easy to fix. If it is not this then it will probally be the board but it will usually only go bad if it has gotten wet. As for where to get parts any pool store can get them if they don't have them on hand or go to your heaters web site and find a retailer through them. I hope this helps, good luck.