What was found
POTABLE WATER IS NOT WORKING AND LAVS STARTING TO BACK UP. ONE HOUR OUT OF LHR WATER PRESSURE WENT TO NO PRESSURE. FOUND AIR COMPRESSOR HAD FAILED. WITH ENGINES/APU RUNNING, BLEED AIR SHOULD HAVE BEEN THE ONE PRESSURIZING THE SYSTEM. THE APU BLEED AIR CHECK VALVE INITIALLY FAILED CAUSING THE AIR COMPRESSOR TO TAKE ON THE LOAD AND CONTINUOUSLY RAN UNTIL IT ALSO FAILED. LHRMM REPLACED THE AIR COMPRESSOR, APU BLEED AIR CHECK VALVE, AND IN-LINE FILTERS. SYSTEM OPERATIONS NORMAL. NOTE: SEVERAL REPORTS FROM OTHER OPERATORS HAVE BEEN RECEIVED ON THE APU BLEED AIR CHECK VALVE FAILING. BOEING HAS A SERVICE BULLETIN TO REPLACED IT WITH A RE-DESIGNED VALVE.