I have the same exact problem with my Cal Spas unit. I had it turned on last night and it was heating and the light was on. I came out and the light had gone off. I thought maybe the bulb was just bad but after letting it run a couple more hours the water did not get any warmer.
The pump seems to be working (I only have one two-speed pump) as water being pumped and flowing as normal. Calsparepair, should I likewise still pull my filter and check for any blockage? If there is none, where do I find the pressure switch at?
Thank you! Nice to google this and find someone who has worked on these things for 20 years.