[Bahamas]

Start at the thru-hill and move forward.

1) Take the strainer cap off then open the seacock. Do you have good flow out of the top of the strainer?
2) Take off the hose that goes from the strainer to the water pump and make sure it's clear.
3) Pull the impeller/replace if necessary.
4) If the impeller was torn up then remove the hose that goes from the pump to the heat exchanger and clear any little rubber parts.
5) Remove the end cap on the heat exchanger and remove any rubber pieces you may find.
6) With the end cap off check the tubes. Do they look blocked or plugged up? If so you may want to take it off and have it cleaned/serviced.

That should get you started