Delta 1300 Series- Cold Water Leak Behind Shower Wall
I have a question on troubleshooting a leak in a remodel installation. Remodeled second floor bathroom- new toilet/tub/tile walls/tub/shower door and new Delta Monitor 1300 series w/ diverter- all installed by remodeling contractor
Three months after installation, I noticed the downstairs bathroom (condo, wet "column" build- downstairs bath under toilet/tub traps) ceiling "soft"- obvious water leakage. I opened up the ceiling and noticed a leak behind the wall coming down when the shower was in use- no matter if shower occupied or just water running - the water appears to be cold water only and is a pretty considerable leak- appears to be too much for leakage through wall. Leak takes about 45 sec-1 minute to develop.
No water leak when shower is off; does not "appear" to leak if tub only used- hard to tell, water is leaking down cold water copper (1/2 type L annealed) riser as well as inside wall.
I have retaped as well as pipe doped shower arm- no effect
Reviewed schematics for Delta 1300 series faucet- can there be a defect that would cause the cold water only leak during shower operation?
Have not taped a tarp to the wall to prevent water splash, but the size of the leak and the fact it happens occupied/unoccupied seems to rule out leak through new tile installation- any suggestions and guidance before I stick it to the remodeler and start ripping out walls?