Diagnosis
The leak occurring around the diverter switch lever on the PUR PLUS PFM400H indicates a failure of the internal O-ring seals or a misalignment of the diverter valve stem. This component is responsible for routing water either through the filter cartridge (filtered) or directly through the spout (unfiltered). When water escapes from the side of the lever rather than the spout, it means the internal seal that isolates the valve stem from the water chamber has perished or shifted. This typically happens due to "water hammer" (sudden pressure spikes in your plumbing) or the degradation of the rubber seals over time due to chlorine exposure. To confirm this is the issue, toggle the lever back and forth several times; if the leak persists regardless of the switch position, the internal gasket is compromised. If the leak only happens in one position, the valve seat may be obstructed by mineral buildup or debris, preventing a watertight seal.
How to Fix It
Because the PFM400H diverter assembly is a factory-sealed unit, you cannot replace a single O-ring inside the lever. The solution is to reset the seating of the unit and, if that fails, replace the filter head. Follow these steps to attempt a manual reset and seal check:
- Turn off the water supply to the faucet completely.
- Remove the filter cartridge by twisting it counter-clockwise to relieve any trapped pressure within the housing.
- Using a soft cloth, wipe down the diverter lever and the area where it meets the plastic housing. Remove any calcium deposits or grit that may be preventing the lever from seating fully.
- Firmly press the diverter lever into its "Filtered" position and hold it for 10 seconds to ensure the internal valve is fully engaged.
- Reinstall the filter cartridge, ensuring it is locked tight with a definitive "click" or full rotation.
- Slowly turn the faucet water back on. If the leak persists at the lever, the internal seal has failed and the entire head assembly must be replaced.
- To replace the head, unscrew the mounting nut from your faucet aerator, slide off the old PFM400H housing, and install the replacement head, ensuring the rubber washer is seated flush against the faucet rim.
If That Didn't Work
- Check the Faucet Aerator Connection: Sometimes the leak appears to be coming from the lever but is actually a "creep" leak from the top mounting nut. Ensure the plastic nut is tightened firmly by hand. If it is loose, water can migrate along the housing and pool around the diverter switch.
- Inspect for Mineral Calcification: If you live in a hard-water area, calcium carbonate can build up inside the valve stem. Soak the entire head assembly (without the filter) in a 50/50 mixture of white vinegar and warm water for two hours. This can dissolve the debris preventing the internal seal from closing.
- Verify Water Pressure: If your home's water pressure exceeds 80 PSI, it can blow out the internal seals of the PFM400H. Install a pressure-reducing valve (PRV) on your main line to prevent the new replacement head from failing in the same manner.
- Check for Cartridge Misalignment: Ensure you are using a genuine PUR PFM series replacement filter. Third-party "compatible" filters often have slightly different dimensions that can put lateral pressure on the diverter valve, causing it to leak from the side.
Heads Up
- Never over-tighten the mounting nut using pliers; the plastic threads on the PFM400H are prone to stripping, which will cause a permanent leak at the faucet connection.
- Always flush a new filter for 60 seconds before using the diverter switch to prevent air pockets from creating pressure spikes that stress the valve seals.
- Avoid using the "Unfiltered" setting for long periods if you have high sediment in your water, as this can lead to buildup inside the diverter mechanism.
- Check the rubber washer at the top of the unit every six months; if it becomes flattened or cracked, it can cause water to bypass the filter and leak around the housing.