This seems to be the most commong problem with Hot Springs spas, but I'm not finding the solution in any post I've read.
About two years ago I started having problems with the red temp light flashing. The first time it happened I called service and they came out to find a relay in the control box had burned (actually burned...turning the board black). They replaced the entire board under warranty and removed some of what was described as 'calcium" from somewhere. The tech left the debris on my patio...it appears to be white crust...shaped like the inside of tube...but wasn't substantial to cause a "flow problem".
About a month after the tech visit, the light started flashing again. My dealer is no help...they just want to send a tech out...won't give me any advice.
Replaced the filters with ceramic,
Replaced both thermisters twice.
Removed the filter at the grey standpipe.
Emptied and refilled placing the hose in the gray standpipe while filling.
When I replace the thermistors the spa works as advertised for about a month and stops again...flashing red light.
The little waterfall works all the time...even when the light is flashing.
if I reset the breakers, the spa will work for about 1/2 hour and stop....and the light will flash again.
I'm not stupid. I can fix this if someone will direct me. Most of what I read indicates this flashing light indicates a "flow" problem or a bad thermistor. The thermistors have been replaced....where should I check for a "flow" problem? As I said...the circulation pump/waterfall works all the time...the jets will work for 1/2 hour after breaker reset.