On 02/03/2021 23:28, 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.

It is a great shame that the website
http://wiki.diyfaq.org.uk
is still down as it includes pressure drop calculations of pipe runs.

If you know the kW of your boiler you would be able to calculate the
size of pipe you actually need. In domestic situations with limited pipe
runs 22mm copper pipe is a safe bet, plus to save embarrassment to Gas
Safe installer Gas Safe have made a blanket requirement to combis where
they must be piped in 22mm. Though I would be happy to have the last
sectionin 15mm.

There is no need for any mechanical protection. The only exception is
using a sheath is through a wall, to ensure that no gas can leak into a
cavity and to stop the chemical effect of mortar. Usually a larger sized
PVC pipe.

Depending on the pipe runs and if the existing pipe is gas tight then
this may be reused. When you say 1/2" steel pipe this normally
corresponds to an internal diameter of 18.6mm if 1/2" BSP.
https://en.wikipedia.org/wiki/British_Standard_Pipe

I believe it is generally said they should not be run in voids. So
behind kitchen units is fine, as is outside. Under floorboards is also
considered a ventilated space.

BICBW