This problem was finally fixed, and I thought I would post this to the forum in case someone may have similar problems. I tried all the remedies to make sure that water and air was not being blocked, but It kept giving me the same HI/PS error at random times. However, after turning off the system, it would restart immediately. This went on until a month ago when it gave up. That is, it would start, run for a couple of seconds, and then display the HI/PS error and quit. If I turned it off and then restarted it, it would do the same. I was advised to replace the water pump (which costs $450 !! - I don't know why it is so expensive), but it turned out that it wasn't the pump. So, I had to call the experts. The a/c guy hooked up the system to his computer, and could not find anything wrong after much searching. He was about to give up, when he discovered that a red live wire had melted on another wire. I am afraid he did not explain to me on the phone which hot wire that was. Apparently, it was not a wire that one can spot easily. For some weird reason it gave the HI/PS error. So, a happy end after many billable hours .. and a working water pump I don't need. Looking back, I could have avoided getting a new water pump, by hooking up the pump directly to an ac plug and observe if water was coming out of the boat. Unfortunately, I did not think of it at that time. Anyway, you cannot always win!! If anybody wants a second-hand pump, please let me know.