[C320-list] Water heater question

[Don Poole]

I'm troubleshooting an engine over temperature issue (200 F) and checked the raw water system intake through pump impeller through discharge and all is good. Dug into the fresh water next. Cleaned the exchanger tubes (they weren't really very bad) checked the thermostat (in a cup of water it opened at the right temp checked with infrared gun and it opened the full stroke per the Perkins shop manual. Just had new hoses installed from the engine to the sink water heater. Anyone ever encounter flow restriction in the water heater? I can't get to the connections ( the boat yard must have had a munchkin connect these). Is there an "IN" and "OUT"? Does it matter ?  I'm trying to thing of anything. Putting the water pump and exchanger tube back in tomorrow. Maybe it will run at closer to 185 F but I just didn't see anything I thought was the answer.