I would check the state of your leisure
battery first as a low
battery will stop the water heater firing up.
A few years ago, we had a problem with our Carver water heater in our old Swift Royale where it would fire up, then shut down after a few seconds. It got progressively worse with the ( I think) red light coming on and failure to light, then eventually it stopped working altogether, no spark, no gas valve opening
I looked online for a replacement burner unit but the only one I could find, new, was a compatable unit called “ Henry”
it came with a new wiring harness and wall switch, so I bought one.
I swapped it all over and it worked fine, for a while ( the water was much hotter than the old one too) , till I noticed a burning smell coming from the boiler area.
I took the burner out and most of the casing had melted and the heat from it had started to burn into the floor under the boiler.
I contacted the seller who told me to get in touch with the importer, which I did, but they did nothing, ignoring all my emails and the customer service and tech dept was always unavailable when I rang.
So, I gave up with them and got my original burner refurbished.
If you find you need a new burner, don’t buy a Henry unit. They are dangerous cheap Chinese rubbish, I‘m pretty sure I was only a few minutes away from a serious fire.
I used arelectronics to repair my old unit. This is them....
https://www.arelectronics.co.uk/contents/en-uk/d23_Carver-Cascade-Gas-Burner-Repairs.html