New Delta 14-Series no water flow

[Conor]

3 months ago I installed a new Basic MultiChoice Rough-in Valve. Capped off the tub and shower with 1/2 iron pipe then and had tile installed.
When I removed Valve cover there was a lot of rust in the water. Almost a sludge.
Installed new Delta Series 14 Cartridge and just a trickel or water flow. Delta service said it must be the cartridge. I relpaced the Cartridge and same thing. Now Delta say it must be the Valve, but I will have to remove tile to replace. I think it unlikely to be the valve. I shut-off the water and poured CLR down from the showerhead line and it seems to come out the Tub spout. After the CLR there is a trickel of water flowing when reassembled, but the improvement might be my imagiation. Still almost zero flow, I am stumped!

 

[Terry]

Do you have pressure to both the hot and cold side? It has balancing, so if one side is off, it shuts down the other side to match it.
Did the valve come with stops? Some valve bodies have stops and some don't. If it does have stops, make sure they are both opened up.

Did you try flushing the valve with the cartridge removed? That would be a two person job, both on phones to communicate with each other, and something to divert water away from the wall like a tube of some sort.
The one on the left has stops.