It has been taking about 3.5-4 hours to bring my spa up to temperature (102 deg.).
I had my pool maintenance guy look at the heater. He checked the sensors and they appear to be fine.
What we noticed is that the heater goes on fine and the "Heating" red LED lights up, but then after anywhere from 10 mins. to much more time the "Service Heater" red LED lights up. However, my maintenance guy says that the unit should typically show a code on the heater that indicates what is wrong and why the "Service Heater" LED has come on. This is not happening.
Any idea what could be wrong with the unit? It is about 8-9 years old.