Quick Answer:
If your shower lost pressure after other plumbing work, start with simple checks: confirm whether the problem is only at the shower or throughout the house, remove and clean the showerhead, and inspect any local shutoff valves. A common fix is to flush the shower valve by removing the cartridge per the manufacturer’s instructions, briefly turning the water on to clear debris, then reinstalling and retesting the cartridge.
Why This Happens
- Debris or solder flux from nearby repairs can dislodge and lodge inside a shower cartridge or showerhead.
- Partially closed service or isolation valves can get bumped during other work.
- Repair work can disturb a pressure‑balancing or thermostatic cartridge, trapping mineral buildup or grit.
- If only one temperature is weak, the problem may be isolated to the hot or cold feed or that side of the valve.
Step-by-Step What to Do
1. Check the rest of the house
- Turn on a sink faucet (hot and cold) elsewhere. If whole‑house pressure is low, the issue isn’t just the shower.
- If only the shower is weak, proceed with the next checks.
2. Determine whether hot or cold is affected
- Run the shower on hot only, then cold only. If one side is noticeably weaker, that narrows the troubleshooting. See Low pressure only on hot side at shower or Low pressure only on cold side at shower for focused checks.
3. Clean the showerhead and remove the aerator screen
- Unscrew the showerhead and run water through the arm to flush visible debris.
- Soak and brush the showerhead filter or screen before reinstalling and testing.
4. Check local shutoff valves and diverter
- Locate any in‑line shutoffs to the shower (if present) and verify they are fully open.
- If your shower has a tub spout diverter, make sure it moves freely; partially stuck diverters can change perceived pressure.
5. Flush the shower valve cartridge (recommended step)
- Turn off the water supply to the shower or to the house as required.
- Remove the handle and trim, then remove the cartridge following the manufacturer’s instructions.
- Place a towel and small bucket under the valve to catch water and debris.
- With the cartridge out, briefly and carefully turn the water back on for a few seconds to flush out grit and solder flakes from the valve body. Keep the flow short to avoid spraying or water damage.
- Turn the water off again, inspect and clean the cartridge if reusable, or replace it if damaged.
- Reinstall the cartridge per the manufacturer’s torque/spec guidance, reassemble the trim, then test the shower.
6. Test and observe
- Run both hot and cold and switch through settings. If pressure returns, the flush likely cleared debris.
- If problems persist, note whether the issue is mechanical (sticking cartridge) or supply‑side (valve, heater, or main line).
What Not to Do
- Don’t overtighten cartridge parts when flushing a valve — overtorquing can crack plastic parts or warp seals and cause leaks.
- Don’t keep trying multiple DIY fixes if pressure doesn’t recover; if flushing and basic checks don’t fix it, a plumber is appropriate to avoid causing further damage.
When to Call a Professional
- If pressure remains low after flushing the valve and cleaning the showerhead.
- If you find broken parts, a cracked cartridge, or if the valve assembly is corroded or stuck.
- If multiple fixtures have low pressure or you suspect the main supply or water heater is the source.
- If you’re uncomfortable removing the cartridge or reassembling the valve to manufacturer specs.
Safety Notes
- Turn off the correct shutoff before disassembly. If unsure, shut off the main water supply.
- Relieve pressure by opening a lower faucet after shutting off water.
- Use eye protection when flushing a valve to avoid spray of debris.
- Keep the valve flush short and controlled; don’t leave the system running with the cartridge out for extended periods.
- Follow the cartridge manufacturer’s instructions for removal and torque on reinstall to avoid damage.
Common Homeowner Questions
- Can debris from other work block my shower?
Yes. Solder, pipe scale, or grit can travel and lodge in the cartridge or showerhead during nearby plumbing work. - Is flushing the valve safe to do myself?
Yes, if you can shut off the supply, follow manufacturer directions, and take basic precautions like eye protection and short flushes. - Will overtightening damage the cartridge?
Yes. Overtightening can crack plastic parts, deform seals, and cause leaks or poor valve operation.