mine is a closed loop, all of ours are. I was told that a in a closed system we can control the water. in a pump n dump your taking harder water with minerals and slowly depositing them in the system, in essence plugging like a radiator get plugged. have someone come and measure flow somehow if they/you can. 800 does seem high.

our bill was higher than it should have been about two months ago.  after that month and a lot of -20 days and nights, service came out and found we were very, very low on refrigerant. and ran a lot of aux heat. water temp was down to 70 or so degrees.  house is smaller, but still working on insulating like it should be. our bill is a lot less than that, somethings not right.