Partial clog after filter install

Quick Answer:

If several taps have reduced flow after fitting a new whole-house filter, don’t panic. Most often the cause is a mis-set bypass valve, trapped debris in the inlet screen or sediment trap, air in the lines, or a clogged cartridge. Check the bypass and cartridge orientation, inspect the inlet screen/sediment trap, bleed the faucets, then compare flow with the filter on and briefly bypassed. If bypassing does not restore normal flow, stop and call the installer.

Why This Happens

When you install a filter you change the flow path and add surfaces that can trap debris. Common reasons for reduced flow right after an install are:

Bypass valve left partially closed or in the wrong position, limiting supply to the house.
Cartridge not seated or installed upside down, so water can’t pass properly through the media.
Small inlet screens or a sediment trap in the housing clogged with loose debris dislodged during installation.
Air trapped in the plumbing after the system was opened — air pockets can reduce or block flow until bled out.
Less commonly, a plumbing cleanout, fitting or valve elsewhere was disturbed or clogged during work. For similar scenarios see **Partial clog after water heater install** and **Partial clog after turning water back on**.

Step-by-Step What to Do

1. Confirm the bypass valve position and cartridge orientation

Find the filter bypass valve (usually a three-way valve or a set of two isolation valves). Verify it is in the position that routes water through the filter, not partly closed. If you meant to bypass, make sure it is fully in bypass. Small misalignments can dramatically cut flow.
Check the cartridge: remove the housing following the manufacturer’s instructions, confirm the cartridge is the right way up and fully seated. Close isolation valves and relieve pressure before opening the housing.

2. Check inlet screens and the sediment trap

Many housings have a small inlet screen or a removable sediment trap at the bottom. Inspect and clean these parts — trapped sand, scale or plumber’s debris can restrict flow.
If the screen is fine but the housing contains cloudy debris, remove and rinse the cartridge area before reseating the cartridge and retesting.

3. Bleed air from faucets

Open a low and a high faucet (for example a basement tap and a second-floor sink) to help air escape. Let water run for a minute or two until flow stabilizes.
Bleeding air can often restore apparent flow that looked poor because of sputtering or intermittent delivery.

4. Observe flow at the cleanout, then briefly bypass the filter to compare

Open a plumbing cleanout or a test faucet upstream of the house supply if you have one, with the filter in service, and note the flow. This gives a simple visual of what the filter allows through.
Then briefly switch the bypass to route water around the filter and observe flow again. A clear improvement when bypassed means the restriction is at the filter assembly or cartridge. If flow does not improve when bypassed, the restriction is elsewhere in the supply line.
Only bypass for short checks. Return valves to their normal positions after testing.

5. Replace or clean the cartridge if it’s clogged

If the cartridge looks visibly clogged, replace it or clean it per the manufacturer’s directions. Some cartridges are disposable and must be replaced.
After replacing or cleaning, reassemble, pressurize the system, bleed air, and recheck flow with and without the bypass.

6. If bypassing doesn’t restore flow, stop and get help

If short bypassing does not restore normal pressure and flow at multiple fixtures, or if you find leaks or damaged fittings, don’t attempt more invasive repairs yourself. Contact the installer or a qualified plumber to diagnose supply-line issues, valves, or pressure regulators.

What Not to Do

Avoid running the house with the bypass closed in hopes the filter will “settle” — that can starve fixtures and stress appliances.
Do not try to force filtration by installing the wrong filter size or cramming the wrong cartridge into the housing. Using incorrect parts can damage the system and reduce flow.
Don’t keep testing indefinitely if bypassing does not restore flow. Call a pro or the installer when flow doesn’t return after bypassing the filter, when pressure drops at several fixtures, or when you detect leaks at the filter connections.
Avoid loosening pressurized fittings without shutting the correct valves and relieving pressure first — that can spray water and cause injury or damage.

When to Call a Professional

If bypassing the filter does not restore normal flow to the house.
If several fixtures show low pressure at the same time and you can’t trace the restriction to the filter.
If you find leaks, a broken valve, or if you are unsure how to safely depressurize and open the filter housing.
If the installer performed the work and the system still behaves poorly, call them to inspect and correct the installation.

Safety Notes

Always shut off the correct isolation valves and relieve pressure before opening a filter housing. Hot water can cause scalding.
Wear gloves and eye protection when handling used cartridges or cleaning sediment traps.
Do not overtighten plastic housings or fittings; follow manufacturer torque guidance to avoid cracking parts.
If you are unsure which valve is which, stop and get help rather than guessing — closing the wrong valve can isolate appliances or cause damage.

Common Homeowner Questions

Why does the flow sometimes come back after a few minutes? Short runs can flush trapped air or loose debris past the restriction; running water can temporarily move material that was blocking the inlet screen.
Can I clean every cartridge and reuse it? Some cartridges are reusable and cleanable, but many are disposable. Check the manufacturer’s instructions and replace disposable cartridges.
Will a pressure regulator problem look like a clogged filter? Yes. A failing regulator or a partly closed main shutoff can reduce pressure to multiple fixtures and may seem like a filter problem; that’s why bypass comparison is useful.