What was found
CLIMBING OUT, WE TURNED ON ALL ANTI-ICE SYSTEMS ENTERING CLOUDS. HAD AN AMBER TAIL ANTI- DISAG WARNING N EIS, FOLLOWED SHORTLY BY LEVEL 2 TAIL A-ICE DISAG. RAN QRH, TURNED OFF SYSTEM AND RETURNED TO DEPARTURE BASE. REPEAT WRITE UP. REMOVED AND REPLACED HORIZONTAL STAB ANTI-ICE SHUTOFF VALVE. REF AMM 30-12-01-4. FLIGHT CREW RAN ENGINE, NO FAULTS.