As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFT NO. 1 BOOST PUMP LOW PRESSURE LIGHT ILLUMINATED ON TAXI PERFORMED QRH PROCEDURE. GROUNDED - YES. REMOVED AND REPLACED NO 1 AFT BOOST PUMP REF B737-800 AMM 28-22-41, NO HELP, REAPPLIED MEL 28-1C. PUMP CHANGE APPEARS TO HAVE FIXED THE ISSUE AFTER R18 BOOST PUMP TANK 1 AFT RELAY WAS RESET REF B737-800 WDM 28-23-11 AND REF AMM 28-22-41-720-802. ALL OPS CHECKS WERE SUCCESSFUL. ALL GROUND VERIFICATION TESTS GOOD.