I refilled hot tub 3 weeks ago. temp never got past 27*. today it sits at 21*. This spring the flo switch casing cracked and I did a homemade fix. there are no error message on the screen (heat icon is on and the pump is flowing water through at a good rate) I replaced the temp sensor in the filter area and the water temp didn’t go back up. could this be a heater issue and needs to be replaced?