New build - boiler fitted with gas leak!

SteadilyClimbing

We bought a new build about 18 months ago, a few months in there was an issue with the boiler (water not getting hot enough). We called the developers (house in still under warranty) who sent out a guy from Vailant. He found a part that needed replacing (he said this shouldn't have passed quality check at the factory) - he replaces it and hot water is restored.
Since we moved in I sometimes get the odd smell of gas, I told this to the Vailant guy who said it was probably just blowing back in from the exhaust pipe outside, and that he couldn't smell any gas. Also said the something along the lines of, it's the burned gas coming from the pipe outside, not "raw" gas, and left it at that (don't quote me on exact wording, but he ultimately said there was no problem as if there was he'd be able to smell gas constantly - which you can't, it's intermittent and fairly irregular.
A year passes, and I still get the odd smell of gas. It's certainly not constant, and only in the utility room where the boiler is (more so out in the back garden where the pipe exits).
We had someone round the other day, and they were in the utility room for a bit. They came out and said there was a "strong" smell of gas, I went in there and couldn't really smell it at all, but called the developers nonetheless and asked them to send someone to check it out.
By this point, we'd also have a water leak from the pipes leading into the boiler, and on two separate occasions had engineers out to firstly find and patch the water leak, and then to repair the wall they had to cut into to find it. Neither time did they mention a smell of gas.
Anyway, chap turned up yesterday to investigate the smell of gas, 2 hours later he's still here, switching between the boiler and the gas main outside (he was doing tests). 
"You're still here?" I said, "I guess you've found something?"
To which he shows me a valve going into the boiler (after he's taken the front off), he said this is the gas main coming in from outside - there is a metal nut on the pipe, which he's swivelling with just his fingers. "You've got a gas leak" he said, explaining that this nut should be so tight you'd struggle to loosen in with a spanner, let alone your fingers.
He'd done tests where he turned the boiler off (bearing in mind the boiler is the only thing that uses gas in the house), and tested the meter, and it was still consuming gas - well, leaking gas.

He's fixed it now, and tested the system for leaks, more than once. He was here hours doing it.
I remarked on how high my gas consumption has been this past year, and he replied that would certainly have been affected.
...and of course, that's not to mention the danger of having gas leak in the house, for a year- my young kids live in this house, it makes me shudder to think what could have happened. 

Where do I stand with this? It's obviously the result of poor servicing. The developer's guy told me yesterday "we'd have tested the system when it was installed, so it couldn't have been like this from day 0" - yet, we've had many many issues with this house that "should have been tested at Day 0" and clearly weren't.
Either way, the blame lies somewhere between the developers, and the Vailant guy.

Am I in a position to demand compensation from this? I mean nobody, thankfully, was injured or harmed (other than my wallet)...

jefaz07

It wouldn’t have been the gas main from outside…maybe the internal pipe work from the meter outside. 

A gas escape that you smell ‘now and then’ would not make you have high consumption so I don’t think you’ll get anywhere with that. 

It is scary having children in the house I agree. I think though that by the time gas gets to explosive limits you’d be able to smell it properly, as well as passers by your house. So you’d know! 

You could ask Vaillant or the last person to touch the boiler - I suspect they will say it was a liking time ago and anything can happen in that period. 

TELLIT01

As it will be impossible to prove when the leak started, I don't think you will get anywhere.  Everybody will say one of the other people who were working on or near the boiler could have knocked the pipe.