Don't know about Ehiems specifically, but for canisters that won't run:
1. check that the impeller is not gummed up/ broken. <Motor may hum & appears to run, but if the impeller is broken, nothing will happen.> This is the most likely reason ... sometimes cleaning with vinegar to get rid of deposits may fix things, or you need a new impeller if broken.
2. Check all seals are airtight.
3. Try running the canister empty (remove all filter baskets, etc.) in case something si obstructing it.
4. check nothing is blocking the hoses.
This si the assembly diagram for the filter .. in case you did not hook it up right: