That's good news but a closed system should be running a 180 degree thermostat and you might want to double check that heat exchanger for a pencil anode. It will look like a 1/4 inch pipe plug on the outside and when you pull it out there won't be anything left on the inside. Should be changed yearly. Good luck with your dive.
Aloha Fish head..if you take a moment and look back through the first few post to this thread a few high ranking members posted that 180-190 is way to high..are you sure about the 180 degree running tempature?