DIAGNOSIS The filter is clogged with sediment or scale. This is the primary sign the filter is exhausted and needs replacement.
FIX Replace the filter. Slow flow means the physical filtration layers are blocked and the ion-exchange resin is saturated. No cleaning will restore flow or performance.
IF THAT DIDN'T WORK Check for an airlock. Remove the reservoir, take out the filter, and rinse it briefly. Reinstall and fill the reservoir. Sometimes reseating it breaks a vacuum seal.
HEADS UP Do not try to speed up flow by poking holes in the filter or using water pressure. It will ruin the filter and contaminate your water.