I'm no plumber but learnt the following: A pipe leaving a boiler should be made of copper for the first meter. See the latest "Construct Ireland " magazine, page 11-17, the article is titled "dead heat".
I can imagine that this is the rule with the bog standard boiler, I connected mine with barrier qualpex straight from the boiler and it was comissioned. But I use a low temperature producing combi condensing boiler for the UFH and the barrier pipe (Qualpex) is certified to take that pressure/temperature.The domestic water pipe is made as well from the same material, no problem so far.
Gas pipe: If you're planning to use LPG then the gas pipe should NOT be made from copper. But I can't tell you the technical reasons for that, I simply don't know them. But it states so in the technical guidance booklet from the various LPG supliers.Though with standard methane gas (Board Gais's product) it would be o.k..