Things You'll Need
OMNI filter tool (if so equipped)
Replacement O ring
Silicone or plumber's grease
Replacement filter cartridge
OMNIfilter produces a line of water filters designed to be installed on the main line where water enters your house. While under-sink water filters treat drinking and dish water, OMNI whole-house filters also protect water conditioners and heaters and remove sediment that can damage showerheads, icemakers and other appliances. The filters have a replaceable cartridge that should be changed every 2 to 3 months. Instructions for changing the cartridges differ from model to model, but all follow these general guidelines.
Fill a container with enough water to clean the filter housing after you remove it. The water supply to the entire house will be interrupted during the process, so plan ahead.
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Turn off the valve on the water line to the filter. Depress the pressure-relief button for a few seconds to allow trapped air to escape.
Unscrew the bottom of the housing and remove it. If your OMNI filter was provided with a special tank wrench, use it to remove the lower housing.
Remove the O-ring seal and inspect it. If it is damaged, replace it with a new one. Otherwise, wipe it clean and set it aside. Remove the old filter from the lower housing. Clean the upper and lower housing with a diluted bleach solution and rinse them thoroughly.
Insert the new cartridge into the lower housing. Lubricate the O-ring seal with silicone or plumber's grease and re-seat it.
Screw the lower housing back onto the upper part until it is hand-tight. Turn the water back on slowly until the valve is fully open. Press the pressure-relief button for a few seconds to vent trapped air.
Turn on a faucet in the house for 15 minutes to flush the new cartridge before using the water.