On Tuesday, 2 March 2021 at 23:28:29 UTC, Nick wrote:
Hello all,

I need to reboiler my place.
The boiler is at least 45 years old and obviously cannot last forever.
I am somewhat older and the same conditions apply.

The supply to existing boiler is 1/2" steel pipe.
I'm told that I need to have a 22mm supply for a new condensing boiler.
The routing of existing pipework cannot be followed without demolishing
about half of the interior of the house. I'm not willing to do that.

Would it be legal to run the majority of the pipework in armoured
rubber/flexible pipe?

The last metre or two at each end would be in metal tubing. All above
ground at high level (2M) and nothing external to the house.

I would appreciate your views.

Many thanks,
Nick.
I'd say no f***ing way - could you expect rubber hose to be gastight in a fire! You really need to determine the actual gas rate of your proposed CONDENSING (not combi) boiler to discover if the steel pipe is adequate[y sized for the job. It might help if you ask someone who knows what they are doing to measure the current boilers gas rate and the pressure drop from meter to boiler under load. This would give you a good idea of the feasibility of reuse. Don't forget steel pipe corroded so it would also be sensible to do a soundness check while he/she is there. I've seen installations in steel pipe where permitted drop increased year on year until it eventually exceeded that allowable. Then it was a case of having to sort it and rerun the pipe in copper.