I remember reading something about this a year or more back. I expect the "by law" is that CORGI will be requiring them to do so. When I put my Keston in, I asked a number of local installers and none had one. You can't adjust the mixture of a condensing boiler without one, which meant they would not have been able to install/commission the boiler properly. I bought my own.
I find it useful with hobs too, to check the CO level in the room. I don't know if gas installers bother with that.
The only thing that's changed recently is that, to use a Combustion Gas Analyser, a gas installer must have a specific qualification ("competence" in gas jargon) for it (which will be shown on their CORGI reg card alongside boilers, gas fires and whatever else they've done assessments in).
It is amazing how often 'law' is invented to assist in marketing. I suspect a strong anti-correlation between inventing law for marketing and abiding by the actual law.
1) It would be pretty difficult to set up and/or check the latest generation of boilers without a combustion analyser. More often than not the makers will require that you use such a tool.
2) There is a competence qualification that has now been introduced in the use of these tools.
3) Some service companies may be insisting on the above qualification for their (boiler) servicing employees.
The law will touch upon the above but there is no explicit law that says "No Analayser no job".
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