Living in Florida, you don't need the fuel heat exchanger IMHO. If I were experiencing your problem and clamping off of the heater hose didn't stop the flow of heat, I would get several feet of heater hose and bypass the entire heater system (4,5,6,7) for the summer months. I'd throw 5 away and put a plug in 4 and 6 for the summer to keep any trash out of the heater system.

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You can't always get what you want, but if you try sometime you just might find you get what you need.