Quick Answer:
Start by checking the new valve and the shower’s internal stops for partial closures or construction debris. Confirm the valve installed is rated for the flow you expected, test the supply and showerhead separately, and clear any debris or restrictors before calling a plumber.
Why This Happens
- New hardware can change flow. Some replacement valves or cartridges are lower-flow or have different sizing than the old parts.
- During a remodel debris, solder, or protective caps can end up inside the valve or piping and block flow.
- Supply shutoff stops may have been left partially closed after work, or a balancing/pressure regulator was adjusted.
- Household pressure can fluctuate for reasons unrelated to the remodel — Shower pressure varies daily with municipal supply or pump cycles.
Step-by-Step What to Do
1. Check other fixtures and overall supply
- Turn on a cold and hot tap at a sink and the bathtub at full. If multiple fixtures are low, it’s a house supply issue, not just the shower.
- Note if pressure varies by time of day; this helps rule in/out municipal supply problems.
2. Confirm the installed valve matches the intended flow rate
- Locate the valve model number or stamp (often on the valve body behind the trim). Compare the valve’s rated flow to what you expected when planning the remodel.
- If the valve is a lower-flow model or has a built-in restrictor, it will limit the shower regardless of pipe size.
3. Check internal stops and supply shutoffs
- Find and operate the internal service stops or isolation valves for the shower (usually behind an access panel). Make sure they are fully open.
- Open the stops briefly and feel for increased flow; a partially closed stop is a common cause after work.
4. Inspect for debris or construction material
- Remove the shower handle and trim to expose the cartridge or valve opening. Look for solder flakes, pipe paste, protective caps, or loose screws.
- With the isolation stops open, briefly remove the cartridge or cover plate and flush the valve to clear debris. Collect water and debris with a towel.
- Reassemble and test flow. If flow improves, debris was likely the cause.
5. Check the showerhead and flow restrictor
- Unscrew the showerhead and test flow from the exposed shower arm. If flow is good there, the head or its restrictor is the issue.
- Clean or temporarily remove the restrictor to test. Reinstall with the correct low-flow parts if required by code or design.
6. Verify cartridge and installation
- If the cartridge was changed during the remodel, confirm it’s the correct model and fully seated. Incorrect cartridges or misaligned seals reduce flow — think of situations like Low pressure after changing cartridge.
- Check for blocked cartridge ports or incorrect orientation that limits flow.
7. If you still have low flow, check regulators and piping
- Locate a whole-house pressure regulator if present; a change in its setting during remodels can reduce shower flow.
- Smaller diameter replacement piping or added restrictive fittings can reduce flow rate; this is when you may need a professional review.
What Not to Do
- Don’t assume remodel changes are cosmetic only; if flow was reduced, a plumber is appropriate.
- Don’t force or pry valve components without identifying the model — you can break seals or void warranties.
- Don’t use a torch or heat on soldered joints while the system is partially assembled or without isolating water — that’s dangerous and can damage fixtures.
When to Call a Professional
- If the installed valve is the wrong size or type for your desired flow and needs replacement.
- If you find restricted piping, incorrect plumbing sizing, or a mis-set pressure regulator.
- If you’re uncomfortable removing cartridges, flushing the valve, or diagnosing hidden shutoffs — a licensed plumber can inspect and correct without risking damage.
Safety Notes
- Always shut off the water supply to the fixture before removing cartridges or valve parts. Open a nearby tap to relieve pressure.
- Watch for hot water when opening lines — drain into a bucket or towel to avoid burns.
- Wear eye protection and gloves when flushing debris. If soldering or making permanent repairs, consider hiring a pro to avoid fire hazards.
Common Homeowner Questions
- Why did pressure drop only after the remodel? Construction often adds debris or a different valve/model that limits flow; check stops and the valve first.
- Can I fix a wrong valve myself? If it’s a simple cartridge swap or reopening a stop, yes; full valve replacement or piping changes are best left to a pro.
- How quickly should a plumber respond? For a total loss of shower flow or suspected incorrect valve, arrange service within a day or two to avoid prolonged inconvenience.