Hatisland

Problem: Presently our Sundance Optima hot tub (circa 2000) will not heat up beyond about 101°F and is showing an intermittent FLO error message. Attempted solutions: Replaced both the temperature sensor and the flow switch Cleaned the filter Primed the pump by loosening the massage selector cap Turned off power to the hot tub for 30 minutes before re-powering Ran hot tub without filter, including running the two speed pump at low Because of the cold weather I have been unable to try putting a hose pipe into the filter pipe and running water into the tub. I saw online a video that suggested slightly loosening the connector where the pipe attaches to the pump and letting out air. I haven't tried this. Perhaps I should? However, there is no problem with the flow of the jets. Observations: The FLO message disappears when the two-speed pumps are running. The FLO message returns when the pumps are stopped The FLO message does not disappear when the single speed pump is running At the moment the temperature indicates 102°F. It is set at 103°F. I have not been able to get the tub to its hottest temperature. In the past, the hottest temperature has been obviously too hot! We left for a week and turned the tub down to 90’F. On returning the temp showed 90’F and the FLO message was absent. I turned the tub up to 102’F, it warmed (I still doubt it was 102’F), but the FLO message returned. Again, FLO disappears as soon as I turn on the first level of the two-speed pump. We have had some residue/deposits (calcium?) accumulating on floor of tub. I’ve tried to clean it out with a net. Wondering if there is more in the pipes and this may be contributing? Any suggestions? Thanks.