The users manual for these pool heaters has a chart that walks you through, step by step, a troubleshooting guide. That is the best way to find a solution to your problem because it asks pretty specific questions that you have to be looking at your heater to answer. Here is a link to the pdf file.
http://www.backyardcitypools.com/images/bwp/Max-E-Therm-Manual.pdf