Yep, its failed. A new run it is - wont be hard to do. Its the new
boiler I'm unhappy about.

Oh, yes there was another appliance run off that section of pipe too. I
guess I had modulation and didnt know it

Ah. Another appliance will drop it much lower!

If the other appliance is greedy, you might even need 28mm to the split and
22mm after. There's no point in underspeccing the new run. Your next boiler
might be a 40kW monster.

Christian.