To pinponint the source of the failure can help you solve the problems by youself, or the factory techs can repair chlornator faster when you provide these infomations.
At First, you need check the phosphates and make certain that the cyanuric acid is up to par If needed, buy the PhosFree treatment and get the reading below 100 PPB. Then, maybe the algae in the shallow areas of the pool, it's easily to attack it now but hard in summer.
After external checks, we need figure out the problem inside of chlornator. First thing is checking the power source and ensure that it is getting power, Not working? check to see if the chlorinator control unit has either a reset button or an internal fuse. push the button or blow the fuse, it can be good now.
Second, you should check if the cell is working well. It's not difficulty to do if your chlornator has a clear cell, if not, as we all know most brands most brands have cells that last about 8,000 hours, some better brands will install the longer life time like 25000 hours, check it and you can find your cell if end of it's life or not, Please not, send it the pool stores is not a cleaver choice.
At last, closely examine the electrical connections between the cell and the control and between the flow switch (if present) and the control. Make these clean and dry.