No less than 18 mb inlet point

[dween]

16.5 on pretty much all worcesters

 

[kris]

He's only got 4m of 22mm plus 4 bends so 6m of 22copper. Having 22mm copper gives you press absorb of 0.4mbar so absolutely fine for gas rate of 3.35m3 so you pressure drop must be @ gas valve / inlet .
But just thinking if you've a hob then your missing hob output and tee piece etc.
Inverness what's the total length of copper as Well as how many gas appliances etc