Sorry to hear about the ongoing nightmare with your heating system. Looking at the list of parts, a few things really don't add up. I've rarely heard of a genuine Webasto having that many serious failures in such a short time. For a start, a split exhaust cannot be caused by the coolant plumbing. That is almost always down to poor installation, vibration fatigue, incorrect sealing, or non-marine-grade parts. The heat exchanger failures are just as suspect—having three fail since 2018 is practically unheard of. It would be useful to know how they actually failed: Splitting: Usually caused by chronic, severe overheating. Corrosion: Caused by having mixed copper and aluminium components in the system without the correct corrosion inhibitor in the coolant. Gaskets: Often caused by improper reassembly during previous repairs, such as reusing old gaskets or fitting incorrect ones. Regarding your engineer’s theory about the pipework: It is difficult to assess properly without seeing the layout, but I don't know how someone could pack enough 90-degree bends into a 60ft narrowboat to stop a Webasto from running correctly. While elbows do add resistance, you would have to install a huge amount of unnecessary bends to cause the circulation pump that much trouble, and pipe routing alone will not cause heat exchangers to leak.