If the canister has been filled up with water before the pump head is clipped into the canister, the unit might have air trapped inside that will cause it not to start. In order to ensure proper function of the unit, please make sure the filter is primed as per the following instructions:
STEP 1: Make sure that there is NO water in the canister. Install all the media, hoses, input and outlet pipes, close up the canister and make sure that all valves are OPEN.
STEP 2: Make sure that the water in the tank is filled up to the top. If your filter does not have a priming aid, i.e. your 2215, and you are using a spray bar, 1) disconnect the spray bar form the output hose and 2) apply a short but strong suction on the OUTLET tube. As you are doing so, keep an eye on the INTAKE tube. As soon as you see water go up the intake and then down the tube on the outside of the tank, STOP applying the suction and now gravity takes over and the water continues to fill up the canister. Immediately re-connect the spray bar to the outlet tube.
NOTE: All that is needed is a short strong suction of a second or two.
STEP 3: If the spray bar or outlet is under the water, it will be bubbling as the air is expelled by the incoming water filling the canister. You may plug in the unit when the bubbling has stopped or when you see that the water has filled up the flexible outlet tubing. NOTE: The water will fill the outlet tubing to approximately 3" to 4" of the top of the tank water level
Note that if you clean the filter and the hoses are still full of water you will not need to prime the unit. You simply need to open the output valve first then open the Intake valve and the unit should fill up by gravity (as long as the canister is empty of water).