Quick Answer:
Whole-house or under-sink filters can crack, leak, or bypass when water pressure or pressure spikes exceed the filter housing rating. Check the housing rating and O-ring seating, measure pressure peaks, install or repair a pressure reducing valve (PRV) and an expansion tank if needed, and add a pressure gauge upstream of the filters to monitor pressure continuously.
Why This Happens
- Filter housings are made of plastic or thin metal and are rated for a maximum working pressure. Repeated high pressure or sudden pressure spikes (water hammer) can crack the housing or force the O-ring out of its groove.
- If the O-ring is misseated, damaged, or dirty the housing can bypass even below the rated pressure because the seal fails.
- System components that fail under high pressure are often related: High pressure ruins solenoid valves and can lead to situations similar to Washing machine hoses bursting. Those failures can create sudden surges or continuous overpressure that damage filter housings.
Step-by-Step What to Do
1. Stop the leak and relieve system pressure
- Close the main shutoff or the supply valve to the filter. Open a faucet downstream to relieve pressure before opening the housing.
- Contain any water with a bucket and towels to avoid floor damage.
2. Check the filter housing rating and condition
- Locate the stamped or printed maximum working pressure on the housing. Note that this is the continuous rating, not a surge tolerance.
- Inspect the housing for hairline cracks, stress lines, or deformation. Replace any damaged housing rather than attempting a temporary repair.
3. Inspect and reseat the O-ring
- Remove the cartridge, lift out the O-ring, clean the groove and the O-ring, and check for cuts or flattening.
- Apply a thin layer of food-grade silicone grease to the O-ring and reseat it squarely in its groove to restore a reliable seal.
4. Measure pressure and capture peaks
- Install a pressure gauge upstream of the filter or attach a temporary gauge to a nearby faucet connection.
- Watch steady-state pressure and observe during events that cause spikes (dishwasher, washing machine fill, irrigation start). For short spikes you may need a pressure logger or a gauge with a maximum-needle indicator to capture peaks.
5. Install or repair a PRV and add an expansion tank
- If measured pressure or spikes exceed the housing rating, install or adjust a PRV so normal pressure stays below the housing rating. Consult the filter manufacturer for a safe setpoint.
- Add or size an expansion tank to absorb thermal expansion and transient spikes in closed systems (especially where a water heater or well pump is present).
- Repair or replace a faulty PRV; don’t rely on the filter housing to resist sustained overpressure.
6. Add a permanent upstream pressure gauge for monitoring
- Install a visible pressure gauge upstream of the filters so you can watch pressure at a glance. Regular checks help catch drift in PRV settings or new pressure sources.
7. Test and document
- Restore supply, pressurize the system slowly, and check for leaks. Operate household appliances to confirm spikes are controlled.
- Record the PRV setting and normal pressure for future reference.
What Not to Do
- Don’t exceed filter housing ratings—overpressure can crack housings and cause flooding.
- Do not use tape or glue as a permanent fix for a cracked housing; replace the housing promptly.
- Don’t ignore repeat or intermittent leaks. A small leak can become a large flood quickly if pressure rises again.
When to Call a Professional
- Call a licensed plumber if you detect hairline cracks, persistent leaks, or if you measure pressure spikes that you can’t eliminate with basic PRV adjustment.
- If you need a PRV installed, a correctly sized expansion tank, or pressure logger setup, a pro can size and place components to code and test for hidden causes such as a failing well pressure switch or thermal expansion issues.
- Get help right away if the leak has caused electrical exposure or significant water damage.
Safety Notes
- Turn off the main water supply and relieve downstream pressure before opening any filter housing.
- Wear eye protection; pressurized water can spray unexpectedly when seals fail.
- Be cautious of electrical components near under-sink areas. If water has contacted outlets or appliances, shut power off and call an electrician if needed.
- Replace damaged parts rather than attempting makeshift fixes that could fail under pressure.
Common Homeowner Questions
- How do I know if pressure caused the problem?
Look for cracks, telltale blowout patterns near fittings, and measure pressure peaks above the housing rating. - Can I just buy a higher-rated housing?
You can upgrade to a higher-rated housing, but first eliminate the cause of spikes (PRV/expansion tank). The system should be controlled, not just beefed up. - Will a PRV stop all pressure spikes?
A properly installed PRV reduces steady pressure and many surges; an expansion tank or specific surge arrestor is often needed for short, sharp spikes.
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For the full directory, see High Pressure Causing Fixture Damage.