If the heater was not winterized properly, you may have a cracked rear header (the first thing to break). Not bad cost and easy to fix. If you left tablets in the chlorinator, then you may have bigger problems.

This is our second season that we have opened the pool. The pool installer actually closed it the first year and when we opened last year something water was leaking. Luckily it was still under warranty. The repairman said that that whoever closed the pool, should have removed the drain plug. Last year it was cracked gaskets. Also last year it a drip, this year water is pouring from the back of the heat exchanger on the left side.

We did remove the plugs last winter. There was no chlorine left in the chlorinator, but I'm almost afraid to say this, but we may have pour some anti-freeze in the chlorinator. My neighbor was helping us close and she was pouring anti-freeze everywhere last winter.

Just how do you winterize a heater? Evidently we are not doing it properly.

That sounds like the rear header. To winterize I usually remove the plugs, let the water drain, and reinstall. Remove the top (8-5/16 screws) and left panel. The crack may be obvious or the header may need to be removed to find what is wrong.

How do you change that?

Sounds like the header cracked but this usually occurs because the plugs weren't removed (usually, "winterizing" the heater simply involves removing these plugs). If you can replace the header yourself, fine. If you have to get a repair company to fix it then its going to cost you. May even want to consider replacement.

DO NOT use regular antifreeze in any of your pool equipment - its pretty much the most toxic product on this earth! If you must use antifreeze, use "RV/Boat" antifreeze whiuch is non-toxic. And don't let your neighbor near your pool!