F&P 918 TD dishwasher. ?

F&P dishwasher: model: 918 TD. There is water remaining in the sump at the bottom of the machine. Why is this so?
I noticed an F1 error message after using the machine for the first time in months (I had been away; there had been visitors staying in my house and they may have used different settings). I cleaned the machine using a degreaser...it went through the cycle correctly, but water remained in the sump.