No Oil Fed to Filter After Filter Change

Hello All - First time poster, long time viewer. I *think* this is going to be an easy one, I just can't figure it out. Here's the scenario. 1. System was functioning perfectly before I touched it 2. Turned Firomatic valve to the closed position located just before the filter 3. Opened the canister and changed the filter 4. Turned Firomatic valve to open position, no oil feed So, the only possible thing I can think of, is that air go into the system during the filter change and any oil that was in the line back-tracked its way back to the tank. The Oil is fed from a tank inside the home on otherside of the basement. The line starts at the base of the tank, makes its way vertically upward to the ceiling, across the basement ceiling and back down to the filter which is seated low to the ground. There is a tigerloop installed after the filter (but that should have nothing to do with my issue).