Boiler,
Kitchen,
Bathroom.
Your old bathroom and kitchen will still work with a new boiler.
The kitchen might need to be altered if you install it before the boiler.
You'll be in the kitchen more frequently than the bathroom.
We had a new boiler fitted in our ten year-old kitchen.
So we went from this. The original boiler fitted at the same time as the kitchen.
To this
Fortunately, I was able to sort it myself.
My wife thought she was going to get a new kitchen!
Wasn't easy, I had to make part of the lower pelmet detachable, as the front of the boiler has to swing down for servicing.
The new "L shaped" fillet that hides the pipework, like the old one I made, just sits on the worktop and can be removed when necessary.