JimH

Thanks for the info. I checked with CalSpa support and I don't have a flow switch on this model. Just the two sensors in the heater. I'll check those with an ohms meter as you suggest above.

Thanks for the advice. Looking into the flow sensor. Will testing the sensors with an ohm meter work if the problem happens sporadically? My thought is I'd only get bad ohm reading at time of failure/shut off. It will be almost impossible for me to catch it happening. Thanks again for the advice.

Checking if anyone has had an issue like this before I change the heater sensors. I've been running the spa at 95 degrees and still get HTR TOO HOT message spradically. The odd thing is it will heat from 65 to 95 just fine. It's only after it starts cycling to maintain 95 that it sporadically gets this message. Trying to figure out if it is the sensors or the mother board. Thanks for any advice.

It's set to standard. Well this model only has 2, 'Ready' and 'Rest'. Ready is normal. Rest will only run during programmed filter cycles. It is in Ready mode. Thanks

I have a Cal Spa Gen II LTR20151000. Model = M-S15-Z630L-B It heats up and runs fine, but at random will stop heating. Simply pushing the heat up or down arrows on the control panel and it will start heating again. May run for Zero to 40 days before it stops heating again. It's like the spa doesn't think the heat needs to come on until you give it some outside coaching (up/down heat arrows). Seems totally random, can occur at any time, colds days or warmer days, so doesn't seem to be related to how much the heater is running.