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.
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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.
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.