I wasn't sure if you had to pass a practical test of competence in soldering the pipes before being let loose on the gas pipes in someones house.
And if you insist
A guesstimate of supply and fit a Vaillant Eco Pro 28kw and the stated pipework through 2 walls mostly a straightish line along the ceilings. The original was about an inch pipe from the meter and changed to 15 mm some where along the length under the floor. My guess is about 2.5 metres before the end as there is a split off pipe there that goes upstairs but it is capped off (old house).
The new boiler fired up and worked but he was muttering something about 900 ppm during a test and said the pipe needed changing. It still failed after doing the pipe. It turned out to be the governor on the meter. I am wondering if that was my problem from the start and I didn't need a new boiler. The old one was an ancient Vaillant Sine 18 T3w, the pilot was on but it wouldn't fire up. Three engineers gave 3 different diagnostics for it. The 2 free ones I ignored as they probably wanted me to have a new boiler anyway and didn't even open it up. The one I paid said there was no power to the circuit boards. As I am qualified in electronics I had a check afterward and there was power everywhere. I decided to replace it anyway as no one wanted to try to repair it. When I called engineers I asked specifically if they knew that type of boiler they said yes, then when they got here said they hadn't seen one before. one tried to blag it and said he knew that type but struggled to open it and then gave up said he wouldn't be able to get the parts and one said all boilers are the same, another I had an argument on the phone about fitting instant electric water heaters which I had done as we had no hot water for over a month while trying to get someone to fix the boiler. I was thinking of just getting a heating only boiler. He said that a 3kw one would burn the wiring in my house and when I said my kettle was 3kw he said no way are they that high, I told him not to bother to come. To save on an electrician I was going to do one 3kw instant zip water heater at the beginning of the pipe then another nearer the tap end as I thought this would probably work better than a single 6kw one. No tank; which he kept banging on about heating a tank of water is costly ignoring what I was saying.
I am not impressed by the local talent(less).