Pls complete your profile which provides the type of equipment and pool you have.
What type of heater is it and how old? How often do you run your heater?
No water should be in any pipe, coil or similar in areas that freeze.
During the swim season, you should run your heater at least every 3-4 weeks. Do not run your heater when the temp is below 60 degrees bc you will get a lot of sweating/condensation that if done a lot, can prematurely wear out your heating elements, that is, for NG and similar type heating systems...