I have a Dimension One -Taos spa that shows the following control panel errors, ICE, COOL, 75degrees, FLO 1.

I have replaced the External heat sensor and the Flow switch, but still get the same errors.

Any suggestions with what I can try next?

ICE and COOL are not issues when the temperature is 75 Degrees, FLO 1 indicates a pressure switch malfunction and therefore the heater does not activate, try bleeding the system of any possible air pockets, provided that does not work then you may need to replace the pressure switch.