Why does my hot tub not heat up ?

For the spa’s heater to operate properly, significant water flow must be
detected within the heater otherwise you may see the dr or dRerror message
displayed. Once this error message has been displayed, your spa will shut
itself down and requires a manual reset to restart it.

Note: check water level is flowing over the filter freely, filters are clean and not over 2 years old (replace if so) and all jets in the spa are open (shut jets will reduce water flow as it will cause water to back up in the plumbing)

If all the checks have been done and the hot tub still will not heat at all, then the MODE
settings maybe on EC/ECN (ECONOMY) or SL/SLP (SLEEP). These modes will only allow the heater to run within their programmed filtration cycle. Reset back to ST/STD (STANDARD) and this will heat spa back to set temperature.

Spa still does not get to temp then is the heater getting power from the pack? An electrician will measure the heater terminals to see if the heater is getting the required voltage.