As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT TOP OF DESCENT (AROUND FL300) WING ANTI-ICE SWITCH WAS SELECTED ON. LEFT VALVE LIGHT ILLUMINATED. TRIED AGAIN AT 10,000 FT AND LEFT VALVE LIGHT ILLUMINATED AGAIN. REFFERED TO QRH. ALTERNATE DEACTIVATION PROCEDURE CW PER CHAP 5-07-01 TABLE 3 ITEM 3. GROUNDED - YES. PERFORMED LEFT WING THERMAL ANTI ICE VALVE HEALTH CHECK PER B737-9 AMM 30-11-11-200-801. 2 CB'S OPENED AND CLOSED. OPS CHECKS NORMAL.