hi there. im wondering if someone can help me. ive got a spa with a pneumatic system in it. must be at least 20 years old. ive gotten it running, rebuilt the pump, replaced the heater element, and thermostat. but the issue still remains.... it wont heat past a certain point! the tub will heat to about 85 - 90 degrees and stop there. im fresh out of ideas on this. please help!