As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU 3 START ATTEMPTS WITH APU FAULT EACH TIME. 99 PERCENT OF FAILED STARTS OCCUR IN DEN USUALLY OK NEXT STA CHECK ALL THE MUSCLE LINES FOR LEAKS & SECURENESS & OF SHUTTLE VALVE INDX 116. FOUND B NUT LOOSE ON SHUTTLE VALVE LINE, SECURED NUT. OPS CHECKED SEVERAL TIMES. APU STARTED AND RAN STRONG.