Quick Answer:
If water pressure in the house is too high or sees sudden spikes, the shower cartridge, balancing spool or valve body can start to seep at the trim plate or diverter. First measure static and peak pressure, fix any pressure control issues, then inspect and replace the cartridge. If leaks continue after replacing the cartridge, check the valve body and stops for scoring from water hammer or pressure-related wear.
Why This Happens
Shower valves contain seals, cartridges and sometimes a balancing spool that react to pressure changes. Continuous high static pressure or brief pressure spikes can deform seals, wear the cartridge and cause the spool to stick or leak. Over time, the repeated stress can also score the metal valve body and shut‑off stops, making leaks persistent even after cartridges are changed. If supply pressure is not corrected first, new seals and cartridges can fail quickly. In some homes, extreme supply pressure can affect other plumbing too — see High pressure warping supply lines for related issues.
Step-by-Step What to Do
1. Shut off water and relieve the system pressure
- Turn off the local shower shutoff stops or the main water supply.
- Open a faucet at the lowest level and the highest fixture to drain remaining water and relieve pressure.
- Make sure no one uses water while you work.
2. Measure static and peak pressure
- Use a simple pressure gauge that screws onto an outdoor hose bib or a washing machine supply connection. Measure static pressure with all fixtures closed; normal is typically 40–60 psi.
- To check for peaks or spikes, observe pressure while a fixture runs (or use a pressure logger). Short, high spikes above 80–100 psi or repeated hammering events indicate a problem.
- If you find high static pressure or spikes, correct pressure before replacing valve internals. A pressure-reducing valve (PRV) or arrestors may be needed.
3. Remove trim and inspect the cartridge and balancing spool
- Carefully remove the handle and trim plate to access the cartridge and spool. Note how parts come out so you can reinstall them correctly.
- Look for cracked plastic, deep scoring, flattened seals, mineral buildup, or a spool that won’t move freely.
- Clean light mineral buildup with vinegar or a recommended cleaner; replace parts with visible damage.
4. Address pressure control before replacing parts
- If a PRV exists, adjust it per manufacturer instructions or have it serviced. If there’s no PRV and static pressure is high, install one or call a plumber to size it correctly.
- Fix water hammer issues with arrestors or by securing pipes; repeated hammering can score valve parts.
- Re-check static and peak pressures after any pressure control work so replacement parts won’t be exposed to the same conditions.
5. Replace the cartridge after pressure is under control
- Buy the exact replacement cartridge or rebuild kit the valve manufacturer specifies.
- With water off and pressure relieved, remove the old cartridge and install the new one, replacing O-rings and seals as needed.
- Turn water back on slowly, check for leaks around the trim and diverter, and test hot/cold balance and diverter operation.
6. If leaks persist, inspect the valve body and stops for scoring
- Look inside the valve body for gouges, deep score marks, or deformed seats where the cartridge seals—these often come from repeated hammering or a loose cartridge.
- Check the in-line shutoff stops for scoring where seals bear; scored metal can prevent a watertight seal even with a new cartridge.
- Severe scoring usually requires valve-body replacement or a professional repair kit; cosmetic cleaning won’t fix structural damage.
What Not to Do
- Don’t rebuild shower valves until pressure is stable—otherwise new seals will fail again.
- Don’t assume a quiet leak is just mineral buildup; persistent seepage after a cartridge change often points to pressure or body damage.
- Don’t overtighten plastic cartridges or use excessive force removing stuck parts; you may break the valve or trim.
When to Call a Professional
- Call a plumber if you cannot reduce static or peak pressure, if pressure spikes persist, or if you suspect the PRV is failing.
- Hire a pro if the valve body or stops show deep scoring, corrosion, or deformations—these repairs usually require experience and sometimes drywall or tile work.
- If multiple fixtures show pressure-related problems or you need advice about a whole-house PRV, a professional assessment is wise. Also consider professional help when warranties may be affected — learn about High pressure voiding appliance warranties.
Safety Notes
- Always shut off water and relieve pressure before disassembling a valve to avoid scalding or water damage.
- Wear gloves and eye protection when working with tools and cleaning agents.
- If soldering, cutting pipe or working in a cramped access area, follow standard safety practices and shut off power if nearby electrical components could get wet.
Common Homeowner Questions
- How high is too high for home water pressure? — Above about 80 psi is often considered too high and can damage fixtures and valves.
- Will a new cartridge fix a leak right away? — Only if pressure is within normal limits and the valve body isn’t damaged; otherwise leaks may return.
- Can I measure peak spikes without special tools? — You can spot some spikes by watching a simple gauge while running fixtures, but a pressure logger gives the best data for intermittent spikes.
Related Articles
If you’re troubleshooting a similar symptom, these guides may help:
For the full directory, see High Pressure Causing Fixture Damage.