no water comes out on the filtered setting, but unfiltered works fine from my faucet.

Diagnosis

The PUR PFM400H is a diverter-style system that relies on a mechanical slide valve to redirect water from the main faucet stream into the filter housing. When you have flow on the "unfiltered" setting but zero flow on "filtered," you are dealing with one of two failures: a complete hydraulic blockage within the filter medium or a mechanical failure of the diverter valve. In most cases, the issue is sediment saturation. Over time, microscopic particles and mineral scale (especially in hard water areas) build up in the filter's pores, eventually creating a physical wall that water cannot penetrate. If the filter is brand new and this is happening, the internal O-rings may be misaligned, creating an airtight seal that prevents water from entering the cartridge. To confirm, check the lever movement; if the lever feels "loose" or doesn't click firmly into the filtered position, the internal diverter pin has likely disconnected or worn down, leaving the valve closed even when the handle is switched.

How to Fix It

Follow these precise steps to isolate and resolve the flow blockage:

1. Turn the diverter lever to the "Unfiltered" position and turn off the faucet completely.
2. Unscrew the filter cartridge by rotating it counter-clockwise. Carefully remove the spent filter and set it aside.
3. With the filter cartridge removed, turn the diverter lever to the "Filtered" position and turn the faucet on slowly.
   • If water sprays out of the open filter housing: The diverter valve is working perfectly, and your previous filter cartridge was completely clogged.
   • If no water comes out of the housing: The diverter valve itself is stuck or broken.
4. If the valve is working, inspect the interior of the filter head for any trapped debris or calcium flakes. Use a cotton swab dipped in white vinegar to clean the contact points where the filter seals.
5. Insert a new PUR PFM400H replacement cartridge. Ensure it is pushed firmly upward into the housing before twisting it clockwise to lock it.
6. With the lever set to "Filtered," run the water for 3 full minutes (approximately 2-3 gallons) to flush out carbon fines and air pockets. This "burping" process is critical to remove air locks that can mimic a total clog.

If That Didn't Work

• Manual Valve Reset: If no water flowed during the "empty housing" test, the diverter pin is stuck. Toggle the lever rapidly between filtered and unfiltered 10-15 times while the water is running. This can often dislodge mineral deposits that are pinning the internal valve in the closed position.
• O-Ring Lubrication: Check the black rubber O-rings on the top of the filter cartridge. If they are dry or pinched, they can create a vacuum seal that prevents water flow. Apply a tiny amount of food-grade silicone grease to the rings to ensure a smooth, airtight fit that allows water to pass through the intake port.
• Aerator Cleaning: Unscrew the faucet aerator (the mesh screen at the tip of the spout). If the aerator is clogged with sediment, the backpressure can prevent the diverter from shifting the water flow effectively. Soak the aerator in vinegar for 30 minutes, scrub with a toothbrush, and reinstall.
• Housing Replacement: If the lever feels completely disconnected from the internal mechanism, the plastic gear inside the PFM400H head has sheared. In this case, the filter cartridge is fine, but the entire faucet-mounted head assembly must be replaced.

Heads Up

• Change Frequency: Replace cartridges every 4 months or 100 gallons. Waiting until the flow stops entirely often causes the diverter valve to stick due to stagnant sediment buildup.
• Air Lock Warning: If you hear a "hissing" sound but see no water, you have an air lock. Keep the water running on the filtered setting for 5 minutes straight to force the air bubble through the carbon block.
• Hard Water Tip: If you live in a high-mineral area, soak the entire filter head (without the cartridge) in a 50/50 vinegar-water solution once a year to prevent calcium buildup from seizing the diverter lever.
• Avoid High Pressure: Do not open the faucet valve to 100% capacity when using the filtered setting; excessive pressure can occasionally cause the internal filter membrane to collapse, leading to a permanent clog.