It has been taking about 3.5-4 hours to bring my spa (I don't have a pool) up to temperature (102 deg.) on a couple of occasions. Of the last four times I have used it, it heated up fine (1.5 hours), the next time took 3.5 hours, the next time 1.5 hours, and most recently 3.5 hours.
I checked out the heater and the "Heating" and "Spa" LED lights up when I turn it on.
Any ideas on what could be the issue or what should be some of the things I evaluate on the heater?