As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSTALLED TKS SYS IAW SK208-174B. DURING FLOW CHECK, FOUND PROPORTIONING VALVE MALFUNCTIONING. INTERNAL CHECK VALVE INOP, LETTING FLUID IN LINES TO PANELS BLEED BACK INTO TANK. IAW OPS CHECK, THE CHECK CAN BE DONE 3 TIMES. THE VALVE FAILED EACH TIME. REPLACED VALVE WITH ANOTHER NEW VALVE WHICH THEN PASSED THE FLOW CHECK. THIS IS THE PROPORTIONING VALVE IN THE AFT FUSELAGE THAT FEEDS THE STABILIZER PANELS.