Step 7 · Test for Leaks
This is a moment of truth. Re-install the valve cartridge that you removed before soldering. Ensure the valve is in the 'off' position. Go to the main water shutoff and turn it on SLOWLY. Listen for any sounds of rushing water. Go back to the access panel and meticulously inspect every single soldered joint for any signs of dripping or moisture. Use a dry paper towel to wipe each joint to make it easier to spot even the smallest leak. If you find a leak, you must shut off the water, drain the lines, and re-solder the faulty joint. Leave the water on for at least 15-20 minutes to be certain everything is watertight.