That happened to us with our 2018 Vegas 24.1 earlier this year ... the water pump wasn’t building enough pressure to keep sufficient flow through the hot water heater. There might have been some air in the line and/or plastic in the water filter. It worked fine when hooked up to city water.
A few weeks later, and after cleaning the pump filter a few times and after some rough road drives, it miraculously started working the night before I took it back to our dealer for warranty work. The dealership checked it out, but couldn’t replicate the issue.
I’ll try the valve suggestion if it happens again.
Fully agree with the comments about running straight hot, no cold.
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