Quick Answer:
If older plastic or CPVC piping shows hairline cracks or weeping, treat it as a pressure problem and act quickly. Immediately verify pressure peaks at the system, reduce static pressure with a PRV and add expansion control, replace any cracked sections, and consider repiping runs that look brittle or are repeatedly stressed. Adding shock arrestors helps reduce sudden pressure spikes that finish off weakened plastic.
Why This Happens
CPVC and older plastic pipes become brittle with age, UV exposure, heat, or chemical attack. When the material is brittle the glued joints and long runs can’t absorb pressure spikes. Sudden valve closures, water heater cycling, or thermal expansion create short-duration peaks that place large stress on the pipe wall and joints. Those repeated shocks produce cracks, slow weeps, or sudden failures.
Because the issue involves pressure behavior as much as material condition, look both at the pipe and at the supply pressure. If you see multiple affected spots, the system is likely experiencing damaging pressure events like rapid closures or hammering. For a deeper look at how spikes affect fittings, see High pressure causing pipe hammer.
Step-by-Step What to Do
1. Stop flowing water and verify the problem
- Shut off the main water and isolate the affected branch if possible.
- Observe the crack or weep. Note location(s), age of runs, and whether they are near the water heater or exposed to sunlight.
- Immediately verify pressure peaks — attach a pressure gauge at an accessible spigot or at the main and check static pressure and any transient spikes. If you don’t have a gauge, keep the system isolated and call a pro for a proper test.
2. Reduce static pressure
- Install a pressure reducing valve (PRV) if the house static pressure is above recommended limits. Aim for a steady 50–60 psi or lower based on appliance requirements; many systems are better at 45–55 psi.
- Add thermal expansion control (an expansion tank) on closed systems so heater cycling doesn’t raise pressure repeatedly.
3. Relieve shock loads
- Add water hammer arrestors at fixtures and near fast-closing valves to cut short-duration spikes that stress joints and pipe walls.
- Where valves cause sudden stops, consider slow-close valves or dampening devices.
4. Replace damaged sections or repipe vulnerable runs
- Cut out any cracked or weeping sections and replace with appropriate materials and properly prepared solvent-weld or transition fittings.
- If runs are old, brittle, or repeatedly failing, consider repiping those runs with a more durable material (PEX or copper) or rerouting away from heat and UV exposure.
- Document which runs were replaced and why; excessive supply pressure can also affect appliances — check related warranty requirements and maintenance guidance in High pressure voiding appliance warranties.
5. Test and monitor
- After repairs and pressure-control devices are in place, perform a pressure test at the new operating pressure and check for leaks over time.
- Re-check pressure readings under different conditions (heater on/off, multiple fixtures running) to confirm spikes are controlled.
What Not to Do
- Don’t ignore CPVC cracking signs—brittle plastic under high pressure can fail catastrophically.
- Don’t cover or hide weeps with tape and assume it’s a long-term fix; that leaves you vulnerable to sudden failure.
- Don’t increase system pressure to “flush” a leak—higher pressure makes cracks worse and can burst fittings.
When to Call a Professional
- Multiple cracks, large leaks, or pressure you can’t control with a PRV you install yourself.
- If you suspect systemic pressure spikes or need a qualified pressure test and transient analysis.
- When repiping long runs, working near structural elements, or making transitions between pipe materials.
- If the leak is causing water damage, or if cutting/repair work would affect gas lines, electrical wiring, or other systems.
Safety Notes
- Always shut off and depressurize the system before cutting or removing pipe. Open a faucet after shutoff to relieve trapped pressure.
- Wear eye protection and gloves when cutting pipe and handling solvents or adhesives.
- Avoid working alone if large leaks are possible; have a second person available or call a pro if you’re unsure.
- Do not heat or flame near solvent-welded joints or plastic piping during repair work.
Common Homeowner Questions
- Q: Can I leave a small crack until a weekend to fix it? A: No. Isolate the branch and shut off supply to that run; brittle cracks can grow quickly under pressure.
- Q: Are clamp-on sleeves a permanent fix? A: No. They may be a temporary stopgap but the correct repair is replacing the damaged section and addressing pressure causes.
- Q: Will lowering my pressure prevent future cracks? A: Yes if combined with arrestors and replacing weakened pipe; pressure control plus replacing brittle sections is the long-term solution.
Related Articles
If you’re troubleshooting a similar symptom, these guides may help:
For the full directory, see High Pressure Causing Fixture Damage.