On 2021-03-03 12:16:53 +0000, Robin said:

On 03/03/2021 11:22, bert wrote:
In article , Robin
writes
On 02/03/2021 23:57, Fredxx wrote:

snip
*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.


I don't want to give false hope to the OP who may well need a new gas pipe.

But I've seen before on some sites that "Gas Safe regulations now state
that gas supply pipes from the meter to a combi boiler must be at least
22mm". Smelt to me like a way to get more work and avoid the bother of
calculating pressure drops.* Gas Safe have no power to make
regulations.* And while the Gas Safety (Installation and Use)
Regulations were amended in 2018 I can't see anything in them about a
minimum pipe size. Have I missed something?


Only that when combi boilers first appeared a lot of installers used
the existing 15mm which was then found to be inadequate.

Thanks but I was aware of that. And it's a bit of a leap from that to
"you *must* use 22mm even if it's a run of 1.5m with one bend to a 24
kW combi". Only makes sense to me if Gas Safe members can no longer be
trusted to do sums and measure pressure drops at existing boiler.

We had a 20 year old 24kWh boiler replaced in the autumn - it was fed
by a fairly long15mm run. To play it safe and not change the pipework
the installer put in a 18kWh unit. As it is a more efficient condensing
boiler it seems to do pretty much the same job as the old one.