I have a 1550 that does everything right in normalize mode yet once I put it in calibration mode the heater stops working. I changed out the thermostats and just about everything else I could think of related to a heater isue..any suggestions why the heater would work in normalize yet not in calibrate mode?

Check your temp sensors WA M, WA C, AB M and AB C. It might be one of your IB01/02 conductivity/temperature boards. Weird problem.

TTech..thanks for the suggestion..I tried that but didnt cure the problem..I guess this is why Baxter will stop servicing these old heaps at the end of the year

Yeah. I might be stuck with them longer than that (gag). When you try to calibrate condo does it ever get past the "TEMP NNNN" part? Do any of them turn "Y"? The reason I'm asking is that they go from, left to right, AB M, AB C, WA M, WA C. This might help to isolate the problem to either the AB or WA. If not a IB01/02 board them maybe a condo cell or even a IB01/02 Monitor or Control ribbon cable. Just a shot in the dark.

TTech...I fixed it. First to answer your question, no all NNNN remained NNNN and would not go to YYYY. This was because the heater would kick off during calibrate mode. What I ended up doing (eventually) was to change out the mother board. This solved the heater issue and it calibrated right up. Like you we also have many 1550's and have to keep them running until our clinics are full of Fresenius K's, so it was imortant for me to figure this one out. I appreciate your input and good luck with yours.