Standard configuration on an in-ground pool with attached spa. The heater is about 19 years old, so owes me nothing. Still heats pool without issues, however when it is heating in spa mode it consistently cuts out every time at approximately 95 or 96 degrees. Then the heater will not re-fire for some period of time. Given the consistency of the temperature at which it cuts out, is this due to some type of faulty switch or coupling which is overheating and can be replaced/repaired? Or is there something else going on? Of course, I can replace the heater but would love to try to avoid spending ~$4000 this summer if I can get another season out of it. Thanks!