f75 code was the first issue.....changed pressure sensor it was the old orange type.so changed that with the new one. filled up and testd now all i get is f73? checked sensor/cable. no break in the wires and the sensor is fine itself..... prior to changing the sensor i unblocked the rubber hoses on the flow & return 2 the heat exchanger.......system is pretty dirty. but still not to sure why im getting a f73 fault. and am going 2 change the rubber hoses 2moz but dont think this will help. im thinkin possibly there is a lot of sludge jsut before the water pressure sensor? any thouights