I don't quite understand why you are having so many problems with the boilers as we have a large number of properties and they seem to have settled down and problems are now quite rare and the response from ROCA engineers very good where it is an emergency we can normaly get an engineer out the same day
We do of course leave power to the boiler and it left in the off position
Most of the problems that you seem to be having, and again this is common, sound like they are more to do with the venting of the boiler
It is well worth having the maintenance contract in place for €65 a year as they first check and service the boiler if they know that they are actually going to come out and have to repair things, afgter 2 years they will chrage for all calls and they check the age of the boiler when they call now
The other main problem is the high water pressure and we often have to turn down the supply pressure as the boier cannot cope with the high pressure in this area
On Canela and Magnolia's you obviously have a solar system which, when working correctly, will normally supply, even at this time of year, enough hot water for a normal days use and if you then have AC installed this is actually a more economical way to heat a property, you need to understand the valve setting, especially turning on the supply to the panel
We always check the boilers a couple of days before somebody arrives and not just turn it on but run the heating and water for a decent testing period and I have 2 at the moment where the gas will not ignite and the boiler engineer will be here later today, normally the regulators will be blocked