Step 6 · Install New Single-Handle Valve
This is the most critical step. First, remove the plastic cartridge from the new valve body to protect it from the heat of soldering. Secure the new single-handle valve to the 2x4 wood block. Dry-fit all the necessary 1/2 inch copper pipe pieces and fittings (like elbows and couplings) to connect the hot inlet, cold inlet, and shower riser outlet of the new valve to the existing pipes. The bottom outlet for the tub spout must be capped with a 1/2 inch copper cap, as single-handle valves typically use the same outlet for both tub and shower, controlled by the diverter on the tub spout. Once everything fits perfectly, disassemble, apply a thin layer of flux to all pipe ends and inside all fittings. Reassemble and use a propane torch to heat each joint, applying lead-free solder until it flows completely around the joint. Use a flame shield behind the pipes to protect the wood stud and block.