The pool and spa cannot be heated at the same time.
The pool will be pre-heated to 78°F (76°F for propane-fueled properties), except during the summer season. The spa is pre-set to 102°F. As mentioned, the pool heater will only heat the pool and spa together (if the waterfall feature is enabled) OR the spa.
Please check and make sure the pool is at 78°F or 76°F, respectively and then switch the heater to spa mode and ensure it is heating up to 102°F upon check-in.