Yes well i thought the clearances around a boiler where smallish say
100 to 200 mm anyway a boiler seems to fit in a 600mm kitchen wall cupboard. Just for servicing access.
This is all a big learning curve here. If I was doing it again I would go to a Spanish "Fonteneria autorizado" and ask them to site and install the boiler and gas bottles and flu and see if they would accept me doing the water pipes and the rads. Of course they really want the whole job.
If you can get anyone to have a look. It seems impossible to get someone to check and safety test your own work. You need a "certiificado de installation" before the gas company will do its own safety checks before they will supply the bottles. This certificate can only be given by an authorized plumber. Having run in a copper gas pipe with soldered joints I found out that the joints need to be braised as Propane eats into solder, so it all had to come out. Now it looks as though I am going to have a major reciting of the boiler and bottles..
I think the message here is clear forget about diy boiler installation. in Spain